staging: fbtft: Rectify GPIO handling

The infamous commit c440eee1a7a1 ("Staging: staging: fbtft: Switch to
the GPIO descriptor interface") broke GPIO handling completely.
It has already four commits to rectify and it seems not enough.
In order to fix the mess here we:

  1) Set default to "inactive" for all requested pins

  2) Fix CS#, RD#, and WR# pins polarity since it's active low
     and GPIO descriptor interface takes it into consideration
     from the Device Tree or ACPI

  3) Consolidate chip activation (CS# assertion) under default
     ->reset() callback

To summarize the expectations about polarity for GPIOs:

   RD#			Low
   WR#			Low
   CS#			Low
   RESET#		Low
   DC or RS		High
   RW			High
   Data	0 .. 15		High

See also Adafruit learning course [1] for the example of the schematics.

While at it, drop unneeded NULL checks, since GPIO API is tolerant to that.

[1]: https://learn.adafruit.com/adafruit-2-8-and-3-2-color-tft-touchscreen-breakout-v2/downloads

Fixes: 92e3e884887c ("Staging: fbtft: Fix GPIO handling")
Fixes: b918d1c27066 ("Staging: fbtft: Fix reset assertion when using gpio descriptor")
Fixes: dbc4f989c878 ("Staging: fbtft: Fix probing of gpio descriptor")
Fixes: c440eee1a7a1 ("Staging: fbtft: Switch to the gpio descriptor interface")
Cc: Jan Sebastian Götte <linux@jaseg.net>
Cc: Nishad Kamdar <nishadkamdar@gmail.com>
Reviewed-by: Phil Reid <preid@electromag.com.au>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210503172114.27891-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 7 deletions

diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
index 4f362dad4436..67c3b1975a4d 100644
--- a/drivers/staging/fbtft/fbtft-core.c
+++ b/drivers/staging/fbtft/fbtft-core.c
@@ -38,8 +38,7 @@ int fbtft_write_buf_dc(struct fbtft_par *par, void *buf, size_t len, int dc)
 {
 	int ret;
 
-	if (par->gpio.dc)
-		gpiod_set_value(par->gpio.dc, dc);
+	gpiod_set_value(par->gpio.dc, dc);
 
 	ret = par->fbtftops.write(par, buf, len);
 	if (ret < 0)
@@ -79,7 +78,7 @@ static int fbtft_request_one_gpio(struct fbtft_par *par,
 	int ret = 0;
 
 	*gpiop = devm_gpiod_get_index_optional(dev, name, index,
-					       GPIOD_OUT_HIGH);
+					       GPIOD_OUT_LOW);
 	if (IS_ERR(*gpiop)) {
 		ret = PTR_ERR(*gpiop);
 		dev_err(dev,
@@ -226,11 +225,15 @@ static void fbtft_reset(struct fbtft_par *par)
 {
 	if (!par->gpio.reset)
 		return;
+
 	fbtft_par_dbg(DEBUG_RESET, par, "%s()\n", __func__);
+
 	gpiod_set_value_cansleep(par->gpio.reset, 1);
 	usleep_range(20, 40);
 	gpiod_set_value_cansleep(par->gpio.reset, 0);
 	msleep(120);
+
+	gpiod_set_value_cansleep(par->gpio.cs, 1);  /* Activate chip */
 }
 
 static void fbtft_update_display(struct fbtft_par *par, unsigned int start_line,
@@ -922,8 +925,6 @@ static int fbtft_init_display_from_property(struct fbtft_par *par)
 		goto out_free;
 
 	par->fbtftops.reset(par);
-	if (par->gpio.cs)
-		gpiod_set_value(par->gpio.cs, 0);  /* Activate chip */
 
 	index = -1;
 	val = values[++index];
@@ -1018,8 +1019,6 @@ int fbtft_init_display(struct fbtft_par *par)
 	}
 
 	par->fbtftops.reset(par);
-	if (par->gpio.cs)
-		gpiod_set_value(par->gpio.cs, 0);  /* Activate chip */
 
 	i = 0;
 	while (i < FBTFT_MAX_INIT_SEQUENCE) {