From 7be865ab8634d4ec2a6bdb9459b268cd60e832af Mon Sep 17 00:00:00 2001 From: "Kim, Milo" Date: Fri, 23 Mar 2012 15:02:01 -0700 Subject: backlight: new backlight driver for LP855x devices THis driver supports TI LP8550/LP8551/LP8552/LP8553/LP8556 backlight devices. The brightness can be controlled by the I2C or PWM input. The lp855x driver provides both modes. For the PWM control, pwm-specific functions can be defined in the platform data. And some information can be read via the sysfs(lp855x device attributes). For details, please refer to Documentation/backlight/lp855x-driver.txt. [axel.lin@gmail.com: add missing mutex_unlock in lp855x_read_byte() error path] [axel.lin@gmail.com: check platform data in lp855x_probe()] [axel.lin@gmail.com: small cleanups] [dan.carpenter@oracle.com: silence a compiler warning] [axel.lin@gmail.com: use id->driver_data to differentiate lp855x chips] [akpm@linux-foundation.org: simplify boolean return expression] Signed-off-by: Milo(Woogyom) Kim Signed-off-by: Axel Lin Signed-off-by: Dan Carpenter Cc: Richard Purdie Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/backlight/lp855x-driver.txt | 78 +++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+) create mode 100644 Documentation/backlight/lp855x-driver.txt (limited to 'Documentation') diff --git a/Documentation/backlight/lp855x-driver.txt b/Documentation/backlight/lp855x-driver.txt new file mode 100644 index 000000000000..f5e4caafab7d --- /dev/null +++ b/Documentation/backlight/lp855x-driver.txt @@ -0,0 +1,78 @@ +Kernel driver lp855x +==================== + +Backlight driver for LP855x ICs + +Supported chips: + Texas Instruments LP8550, LP8551, LP8552, LP8553 and LP8556 + +Author: Milo(Woogyom) Kim + +Description +----------- + +* Brightness control + +Brightness can be controlled by the pwm input or the i2c command. +The lp855x driver supports both cases. + +* Device attributes + +1) bl_ctl_mode +Backlight control mode. +Value : pwm based or register based + +2) chip_id +The lp855x chip id. +Value : lp8550/lp8551/lp8552/lp8553/lp8556 + +Platform data for lp855x +------------------------ + +For supporting platform specific data, the lp855x platform data can be used. + +* name : Backlight driver name. If it is not defined, default name is set. +* mode : Brightness control mode. PWM or register based. +* device_control : Value of DEVICE CONTROL register. +* initial_brightness : Initial value of backlight brightness. +* pwm_data : Platform specific pwm generation functions. + Only valid when brightness is pwm input mode. + Functions should be implemented by PWM driver. + - pwm_set_intensity() : set duty of PWM + - pwm_get_intensity() : get current duty of PWM +* load_new_rom_data : + 0 : use default configuration data + 1 : update values of eeprom or eprom registers on loading driver +* size_program : Total size of lp855x_rom_data. +* rom_data : List of new eeprom/eprom registers. + +example 1) lp8552 platform data : i2c register mode with new eeprom data + +#define EEPROM_A5_ADDR 0xA5 +#define EEPROM_A5_VAL 0x4f /* EN_VSYNC=0 */ + +static struct lp855x_rom_data lp8552_eeprom_arr[] = { + {EEPROM_A5_ADDR, EEPROM_A5_VAL}, +}; + +static struct lp855x_platform_data lp8552_pdata = { + .name = "lcd-bl", + .mode = REGISTER_BASED, + .device_control = I2C_CONFIG(LP8552), + .initial_brightness = INITIAL_BRT, + .load_new_rom_data = 1, + .size_program = ARRAY_SIZE(lp8552_eeprom_arr), + .rom_data = lp8552_eeprom_arr, +}; + +example 2) lp8556 platform data : pwm input mode with default rom data + +static struct lp855x_platform_data lp8556_pdata = { + .mode = PWM_BASED, + .device_control = PWM_CONFIG(LP8556), + .initial_brightness = INITIAL_BRT, + .pwm_data = { + .pwm_set_intensity = platform_pwm_set_intensity, + .pwm_get_intensity = platform_pwm_get_intensity, + }, +}; -- cgit v1.2.3 From 5ae4e8a77dc82afcfe8460168ec0b94f4b79a54a Mon Sep 17 00:00:00 2001 From: "Kim, Milo" Date: Fri, 23 Mar 2012 15:02:08 -0700 Subject: drivers/leds/leds-lp5521.c: add 'name' in the lp5521_led_config The name of each led channel can be configurable. For the compatibility, the name is set to default value(xx:channelN) when 'name' is not defined. Signed-off-by: Milo(Woogyom) Kim Acked-by: Linus Walleij Cc: Arun MURTHY Cc: Srinidhi Kasagar Cc: Richard Purdie Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/leds/leds-lp5521.txt | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'Documentation') diff --git a/Documentation/leds/leds-lp5521.txt b/Documentation/leds/leds-lp5521.txt index c4d8d151e0fe..f48ab757d120 100644 --- a/Documentation/leds/leds-lp5521.txt +++ b/Documentation/leds/leds-lp5521.txt @@ -43,17 +43,23 @@ Format: 10x mA i.e 10 means 1.0 mA example platform data: Note: chan_nr can have values between 0 and 2. +The name of each channel can be configurable. +If the name field is not defined, the default name will be set to 'xxxx:channelN' +(XXXX : pdata->label or i2c client name, N : channel number) static struct lp5521_led_config lp5521_led_config[] = { { + .name = "red", .chan_nr = 0, .led_current = 50, .max_current = 130, }, { + .name = "green", .chan_nr = 1, .led_current = 0, .max_current = 130, }, { + .name = "blue", .chan_nr = 2, .led_current = 0, .max_current = 130, -- cgit v1.2.3 From 3b49aacd0e56d5bf1b511f6554f17cd65eb8da64 Mon Sep 17 00:00:00 2001 From: "Kim, Milo" Date: Fri, 23 Mar 2012 15:02:08 -0700 Subject: drivers/leds/leds-lp5521.c: add 'update_config' in the lp5521_platform_data The value of CONFIG register(Addr 08h) is configurable. For supporting this feature, update_config is added in the platform data. If 'update_config' is not defined, the default value is 'LP5521_PWRSAVE_EN | LP5521_CP_MODE_AUTO | LP5521_R_TO_BATT'. To define CONFIG register in the platform data, the bit definitions were mo= ved to the header file. Documentation updated : description about 'update_config' and example. Signed-off-by: Milo(Woogyom) Kim Acked-by: Linus Walleij Cc: Arun MURTHY Cc: Srinidhi Kasagar Cc: Richard Purdie Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/leds/leds-lp5521.txt | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'Documentation') diff --git a/Documentation/leds/leds-lp5521.txt b/Documentation/leds/leds-lp5521.txt index f48ab757d120..e3c66c64591d 100644 --- a/Documentation/leds/leds-lp5521.txt +++ b/Documentation/leds/leds-lp5521.txt @@ -92,3 +92,22 @@ static struct lp5521_platform_data lp5521_platform_data = { If the current is set to 0 in the platform data, that channel is disabled and it is not visible in the sysfs. + +The 'update_config' : CONFIG register (ADDR 08h) +This value is platform-specific data. +If update_config is not defined, the CONFIG register is set with +'LP5521_PWRSAVE_EN | LP5521_CP_MODE_AUTO | LP5521_R_TO_BATT'. +(Enable auto-powersave, set charge pump to auto, red to battery) + +example of update_config : + +#define LP5521_CONFIGS (LP5521_PWM_HF | LP5521_PWRSAVE_EN | \ + LP5521_CP_MODE_AUTO | LP5521_R_TO_BATT | \ + LP5521_CLK_INT) + +static struct lp5521_platform_data lp5521_pdata = { + .led_config = lp5521_led_config, + .num_channels = ARRAY_SIZE(lp5521_led_config), + .clock_mode = LP5521_CLOCK_INT, + .update_config = LP5521_CONFIGS, +}; -- cgit v1.2.3 From 011af7bc7cd188a0310e2d26cdc2cc5d90148b0c Mon Sep 17 00:00:00 2001 From: "Kim, Milo" Date: Fri, 23 Mar 2012 15:02:09 -0700 Subject: drivers/leds/leds-lp5521.c: support led pattern data The lp5521 has autonomous operation mode without external control. Using lp5521_platform_data, various led patterns can be configurable. For supporting this feature, new functions and device attribute are added. Structure of lp5521_led_pattern: 3 channels are supported - red, green and blue. Pattern(s) of each channel and numbers of pattern(s) are defined in the pla= tform data. Pattern data are hexa codes which include pattern commands such like set pwm, wait, ramp up/down, branch and so on. Pattern mode functions: * lp5521_clear_program_memory Before running new led pattern, program memory should be cleared. * lp5521_write_program_memory Pattern data updated in the program memory via the i2c. * lp5521_get_pattern Get pattern from predefined in the platform data. * lp5521_run_led_pattern Stop current pattern or run new pattern. Transition time is required between different operation mode. Device attribute - 'led_pattern': To load specific led pattern, new device attribute is added. When the lp5521 driver is unloaded, stop current led pattern mode. Documentation updated : description about how to define the led patterns and example. [akpm@linux-foundation.org: checkpatch fixes] Signed-off-by: Milo(Woogyom) Kim Acked-by: Linus Walleij Cc: Arun MURTHY Cc: Srinidhi Kasagar Cc: Richard Purdie Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/leds/leds-lp5521.txt | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) (limited to 'Documentation') diff --git a/Documentation/leds/leds-lp5521.txt b/Documentation/leds/leds-lp5521.txt index e3c66c64591d..0e542ab3d4a0 100644 --- a/Documentation/leds/leds-lp5521.txt +++ b/Documentation/leds/leds-lp5521.txt @@ -111,3 +111,41 @@ static struct lp5521_platform_data lp5521_pdata = { .clock_mode = LP5521_CLOCK_INT, .update_config = LP5521_CONFIGS, }; + +LED patterns : LP5521 has autonomous operation without external control. +Pattern data can be defined in the platform data. + +example of led pattern data : + +/* RGB(50,5,0) 500ms on, 500ms off, infinite loop */ +static u8 pattern_red[] = { + 0x40, 0x32, 0x60, 0x00, 0x40, 0x00, 0x60, 0x00, + }; + +static u8 pattern_green[] = { + 0x40, 0x05, 0x60, 0x00, 0x40, 0x00, 0x60, 0x00, + }; + +static struct lp5521_led_pattern board_led_patterns[] = { + { + .r = pattern_red, + .g = pattern_green, + .size_r = ARRAY_SIZE(pattern_red), + .size_g = ARRAY_SIZE(pattern_green), + }, +}; + +static struct lp5521_platform_data lp5521_platform_data = { + .led_config = lp5521_led_config, + .num_channels = ARRAY_SIZE(lp5521_led_config), + .clock_mode = LP5521_CLOCK_EXT, + .patterns = board_led_patterns, + .num_patterns = ARRAY_SIZE(board_led_patterns), +}; + +Then predefined led pattern(s) can be executed via the sysfs. +To start the pattern #1, +# echo 1 > /sys/bus/i2c/devices/xxxx/led_pattern +(xxxx : i2c bus & slave address) +To end the pattern, +# echo 0 > /sys/bus/i2c/devices/xxxx/led_pattern -- cgit v1.2.3 From fbedceb10066430b925cf43fbf926e8abb9e2359 Mon Sep 17 00:00:00 2001 From: Bob Pearson Date: Fri, 23 Mar 2012 15:02:22 -0700 Subject: crc32: move long comment about crc32 fundamentals to Documentation/ Move a long comment from lib/crc32.c to Documentation/crc32.txt where it will more likely get read. Edited the resulting document to add an explanation of the slicing-by-n algorithm. [djwong@us.ibm.com: minor changelog tweaks] [akpm@linux-foundation.org: fix typo, per George] Signed-off-by: George Spelvin Signed-off-by: Bob Pearson Signed-off-by: Darrick J. Wong Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/00-INDEX | 2 + Documentation/crc32.txt | 182 ++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 184 insertions(+) create mode 100644 Documentation/crc32.txt (limited to 'Documentation') diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX index a1a643272883..2214f123a976 100644 --- a/Documentation/00-INDEX +++ b/Documentation/00-INDEX @@ -104,6 +104,8 @@ cpuidle/ - info on CPU_IDLE, CPU idle state management subsystem. cputopology.txt - documentation on how CPU topology info is exported via sysfs. +crc32.txt + - brief tutorial on CRC computation cris/ - directory with info about Linux on CRIS architecture. crypto/ diff --git a/Documentation/crc32.txt b/Documentation/crc32.txt new file mode 100644 index 000000000000..a08a7dd9d625 --- /dev/null +++ b/Documentation/crc32.txt @@ -0,0 +1,182 @@ +A brief CRC tutorial. + +A CRC is a long-division remainder. You add the CRC to the message, +and the whole thing (message+CRC) is a multiple of the given +CRC polynomial. To check the CRC, you can either check that the +CRC matches the recomputed value, *or* you can check that the +remainder computed on the message+CRC is 0. This latter approach +is used by a lot of hardware implementations, and is why so many +protocols put the end-of-frame flag after the CRC. + +It's actually the same long division you learned in school, except that +- We're working in binary, so the digits are only 0 and 1, and +- When dividing polynomials, there are no carries. Rather than add and + subtract, we just xor. Thus, we tend to get a bit sloppy about + the difference between adding and subtracting. + +Like all division, the remainder is always smaller than the divisor. +To produce a 32-bit CRC, the divisor is actually a 33-bit CRC polynomial. +Since it's 33 bits long, bit 32 is always going to be set, so usually the +CRC is written in hex with the most significant bit omitted. (If you're +familiar with the IEEE 754 floating-point format, it's the same idea.) + +Note that a CRC is computed over a string of *bits*, so you have +to decide on the endianness of the bits within each byte. To get +the best error-detecting properties, this should correspond to the +order they're actually sent. For example, standard RS-232 serial is +little-endian; the most significant bit (sometimes used for parity) +is sent last. And when appending a CRC word to a message, you should +do it in the right order, matching the endianness. + +Just like with ordinary division, you proceed one digit (bit) at a time. +Each step of the division you take one more digit (bit) of the dividend +and append it to the current remainder. Then you figure out the +appropriate multiple of the divisor to subtract to being the remainder +back into range. In binary, this is easy - it has to be either 0 or 1, +and to make the XOR cancel, it's just a copy of bit 32 of the remainder. + +When computing a CRC, we don't care about the quotient, so we can +throw the quotient bit away, but subtract the appropriate multiple of +the polynomial from the remainder and we're back to where we started, +ready to process the next bit. + +A big-endian CRC written this way would be coded like: +for (i = 0; i < input_bits; i++) { + multiple = remainder & 0x80000000 ? CRCPOLY : 0; + remainder = (remainder << 1 | next_input_bit()) ^ multiple; +} + +Notice how, to get at bit 32 of the shifted remainder, we look +at bit 31 of the remainder *before* shifting it. + +But also notice how the next_input_bit() bits we're shifting into +the remainder don't actually affect any decision-making until +32 bits later. Thus, the first 32 cycles of this are pretty boring. +Also, to add the CRC to a message, we need a 32-bit-long hole for it at +the end, so we have to add 32 extra cycles shifting in zeros at the +end of every message, + +These details lead to a standard trick: rearrange merging in the +next_input_bit() until the moment it's needed. Then the first 32 cycles +can be precomputed, and merging in the final 32 zero bits to make room +for the CRC can be skipped entirely. This changes the code to: + +for (i = 0; i < input_bits; i++) { + remainder ^= next_input_bit() << 31; + multiple = (remainder & 0x80000000) ? CRCPOLY : 0; + remainder = (remainder << 1) ^ multiple; +} + +With this optimization, the little-endian code is particularly simple: +for (i = 0; i < input_bits; i++) { + remainder ^= next_input_bit(); + multiple = (remainder & 1) ? CRCPOLY : 0; + remainder = (remainder >> 1) ^ multiple; +} + +The most significant coefficient of the remainder polynomial is stored +in the least significant bit of the binary "remainder" variable. +The other details of endianness have been hidden in CRCPOLY (which must +be bit-reversed) and next_input_bit(). + +As long as next_input_bit is returning the bits in a sensible order, we don't +*have* to wait until the last possible moment to merge in additional bits. +We can do it 8 bits at a time rather than 1 bit at a time: +for (i = 0; i < input_bytes; i++) { + remainder ^= next_input_byte() << 24; + for (j = 0; j < 8; j++) { + multiple = (remainder & 0x80000000) ? CRCPOLY : 0; + remainder = (remainder << 1) ^ multiple; + } +} + +Or in little-endian: +for (i = 0; i < input_bytes; i++) { + remainder ^= next_input_byte(); + for (j = 0; j < 8; j++) { + multiple = (remainder & 1) ? CRCPOLY : 0; + remainder = (remainder >> 1) ^ multiple; + } +} + +If the input is a multiple of 32 bits, you can even XOR in a 32-bit +word at a time and increase the inner loop count to 32. + +You can also mix and match the two loop styles, for example doing the +bulk of a message byte-at-a-time and adding bit-at-a-time processing +for any fractional bytes at the end. + +To reduce the number of conditional branches, software commonly uses +the byte-at-a-time table method, popularized by Dilip V. Sarwate, +"Computation of Cyclic Redundancy Checks via Table Look-Up", Comm. ACM +v.31 no.8 (August 1998) p. 1008-1013. + +Here, rather than just shifting one bit of the remainder to decide +in the correct multiple to subtract, we can shift a byte at a time. +This produces a 40-bit (rather than a 33-bit) intermediate remainder, +and the correct multiple of the polynomial to subtract is found using +a 256-entry lookup table indexed by the high 8 bits. + +(The table entries are simply the CRC-32 of the given one-byte messages.) + +When space is more constrained, smaller tables can be used, e.g. two +4-bit shifts followed by a lookup in a 16-entry table. + +It is not practical to process much more than 8 bits at a time using this +technique, because tables larger than 256 entries use too much memory and, +more importantly, too much of the L1 cache. + +To get higher software performance, a "slicing" technique can be used. +See "High Octane CRC Generation with the Intel Slicing-by-8 Algorithm", +ftp://download.intel.com/technology/comms/perfnet/download/slicing-by-8.pdf + +This does not change the number of table lookups, but does increase +the parallelism. With the classic Sarwate algorithm, each table lookup +must be completed before the index of the next can be computed. + +A "slicing by 2" technique would shift the remainder 16 bits at a time, +producing a 48-bit intermediate remainder. Rather than doing a single +lookup in a 65536-entry table, the two high bytes are looked up in +two different 256-entry tables. Each contains the remainder required +to cancel out the corresponding byte. The tables are different because the +polynomials to cancel are different. One has non-zero coefficients from +x^32 to x^39, while the other goes from x^40 to x^47. + +Since modern processors can handle many parallel memory operations, this +takes barely longer than a single table look-up and thus performs almost +twice as fast as the basic Sarwate algorithm. + +This can be extended to "slicing by 4" using 4 256-entry tables. +Each step, 32 bits of data is fetched, XORed with the CRC, and the result +broken into bytes and looked up in the tables. Because the 32-bit shift +leaves the low-order bits of the intermediate remainder zero, the +final CRC is simply the XOR of the 4 table look-ups. + +But this still enforces sequential execution: a second group of table +look-ups cannot begin until the previous groups 4 table look-ups have all +been completed. Thus, the processor's load/store unit is sometimes idle. + +To make maximum use of the processor, "slicing by 8" performs 8 look-ups +in parallel. Each step, the 32-bit CRC is shifted 64 bits and XORed +with 64 bits of input data. What is important to note is that 4 of +those 8 bytes are simply copies of the input data; they do not depend +on the previous CRC at all. Thus, those 4 table look-ups may commence +immediately, without waiting for the previous loop iteration. + +By always having 4 loads in flight, a modern superscalar processor can +be kept busy and make full use of its L1 cache. + +Two more details about CRC implementation in the real world: + +Normally, appending zero bits to a message which is already a multiple +of a polynomial produces a larger multiple of that polynomial. Thus, +a basic CRC will not detect appended zero bits (or bytes). To enable +a CRC to detect this condition, it's common to invert the CRC before +appending it. This makes the remainder of the message+crc come out not +as zero, but some fixed non-zero value. (The CRC of the inversion +pattern, 0xffffffff.) + +The same problem applies to zero bits prepended to the message, and a +similar solution is used. Instead of starting the CRC computation with +a remainder of 0, an initial remainder of all ones is used. As long as +you start the same way on decoding, it doesn't make a difference. -- cgit v1.2.3