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author | Hans de Goede <hdegoede@redhat.com> | 2015-01-24 12:56:31 +0100 |
---|---|---|
committer | Maxime Ripard <maxime.ripard@free-electrons.com> | 2015-01-25 16:55:13 +0100 |
commit | 6424e0aeebc4d21f14d5bfcbc8436c2836c38a75 (patch) | |
tree | f307b79462ed2e9b332603002d779c3dbc2462b4 /drivers/clk/sunxi | |
parent | 7a6fca879f59824963cd456d8cc5db24ac5acfc0 (diff) | |
download | linux-6424e0aeebc4d21f14d5bfcbc8436c2836c38a75.tar.gz linux-6424e0aeebc4d21f14d5bfcbc8436c2836c38a75.tar.bz2 linux-6424e0aeebc4d21f14d5bfcbc8436c2836c38a75.zip |
clk: sunxi: rewrite sun9i_a80_get_pll4_factors()
The old implementation of sun9i_a80_get_pll4_factors() has several issues,
it checks against 256 / 512 in various places where it should use 255 / 511,
it does the wrong thing for low frequencies which are an even multiple of
6 MHz, e.g. if you ask it for 72 MHz it will result in 144 Mhz, and it does
not take into account that n must be at least 12. Moreover it is quite hard
to read / follow it.
This commit rewrites it to be correct in all cases, and makes it much easier
to follow the code / to read.
Cc: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Diffstat (limited to 'drivers/clk/sunxi')
-rw-r--r-- | drivers/clk/sunxi/clk-sun9i-core.c | 57 |
1 files changed, 29 insertions, 28 deletions
diff --git a/drivers/clk/sunxi/clk-sun9i-core.c b/drivers/clk/sunxi/clk-sun9i-core.c index 9b5e7a1f72d0..d8da77d72861 100644 --- a/drivers/clk/sunxi/clk-sun9i-core.c +++ b/drivers/clk/sunxi/clk-sun9i-core.c @@ -24,50 +24,51 @@ /** - * sun9i_a80_get_pll4_factors() - calculates n, p, m factors for PLL1 + * sun9i_a80_get_pll4_factors() - calculates n, p, m factors for PLL4 * PLL4 rate is calculated as follows * rate = (parent_rate * n >> p) / (m + 1); - * parent_rate is always 24Mhz + * parent_rate is always 24MHz * * p and m are named div1 and div2 in Allwinner's SDK */ static void sun9i_a80_get_pll4_factors(u32 *freq, u32 parent_rate, - u8 *n, u8 *k, u8 *m, u8 *p) + u8 *n_ret, u8 *k, u8 *m_ret, u8 *p_ret) { - int div; + int n; + int m = 1; + int p = 1; - /* Normalize value to a 6M multiple */ - div = DIV_ROUND_UP(*freq, 6000000); + /* Normalize value to a 6 MHz multiple (24 MHz / 4) */ + n = DIV_ROUND_UP(*freq, 6000000); - /* divs above 256 cannot be odd */ - if (div > 256) - div = round_up(div, 2); + /* If n is too large switch to steps of 12 MHz */ + if (n > 255) { + m = 0; + n = (n + 1) / 2; + } + + /* If n is still too large switch to steps of 24 MHz */ + if (n > 255) { + p = 0; + n = (n + 1) / 2; + } - /* divs above 512 must be a multiple of 4 */ - if (div > 512) - div = round_up(div, 4); + /* n must be between 12 and 255 */ + if (n > 255) + n = 255; + else if (n < 12) + n = 12; - *freq = 6000000 * div; + *freq = ((24000000 * n) >> p) / (m + 1); /* we were called to round the frequency, we can now return */ - if (n == NULL) + if (n_ret == NULL) return; - /* p will be 1 for divs under 512 */ - if (div < 512) - *p = 1; - else - *p = 0; - - /* m will be 1 if div is odd */ - if (div & 1) - *m = 1; - else - *m = 0; - - /* calculate a suitable n based on m and p */ - *n = div / (*p + 1) / (*m + 1); + *n_ret = n; + *m_ret = m; + *p_ret = p; } static struct clk_factors_config sun9i_a80_pll4_config = { |