linux-kernel - Re: [BUG] SPI broken for SPI based panel drivers

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Message-ID: <CAGngYiVd6d2pb3eOd5ZiCvTBOzZK6+dudRUVWj8neBRK0S42Pg@mail.gmail.com>
Date:   Tue, 1 Dec 2020 10:52:03 -0500
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: [BUG] SPI broken for SPI based panel drivers

Nikolaus,

On Tue, Dec 1, 2020 at 9:38 AM H. Nikolaus Schaller <hns@...delico.com> wrote:
>
> Let's work on a fix for the fix now.

I tested spi-gpio on my system, by converting a built-in or hardware spi,
to a spi-gpio. Interestingly, the patch has the opposite effect on my system:
before the patch, spi-gpio did not work, but after it's applied, it does work.

Can you tell me the idle status of your chip-select gpio in debugfs?
# mount -t debugfs none /sys/kernel/debug
# cat /sys/kernel/debug/gpio
Look for something like this:
gpiochip0: GPIOs 0-31, parent: platform/209c000.gpio, 209c000.gpio:
 gpio-17  (                    |spi5 CS0            ) out hi ACTIVE LOW

Also, apply the following patch, and tell me
a) does this dev_err() get called on your system, and
b) what is the value when your chip is de-selected

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 7e8804b02be9..b2f4cf5c9ffb 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -813,11 +813,12 @@ static void spi_set_cs(struct spi_device *spi,
bool enable)

        if (spi->cs_gpiod || gpio_is_valid(spi->cs_gpio)) {
                if (!(spi->mode & SPI_NO_CS)) {
-                       if (spi->cs_gpiod)
+                       if (spi->cs_gpiod) {
+                               dev_err(&spi->dev, "gpiod %s", enable1
? "enable" : "disable");
                                /* polarity handled by gpiolib */
                                gpiod_set_value_cansleep(spi->cs_gpiod,
                                                         enable1);
-                       else
+                       } else
                                /*
                                 * invert the enable line, as active low is
                                 * default for SPI.