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SubjectRe: [BUG] SPI broken for SPI based panel drivers
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> Am 01.12.2020 um 16:52 schrieb Sven Van Asbroeck <thesven73@gmail.com>:
>
> Nikolaus,
>
> On Tue, Dec 1, 2020 at 9:38 AM H. Nikolaus Schaller <hns@goldelico.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

root@letux:~# mount -t debugfs none /sys/kernel/debug
root@letux:~# cat /sys/kernel/debug/gpio|fgrep spi
gpio-179 ( |spi4 CS0 ) out lo
root@letux:~#

That is after the panel driver did send the commands.

>
> Also, apply the following patch, and tell me
> a) does this dev_err() get called on your system, and

yes. Many times.

> b) what is the value when your chip is de-selected

root@letux:~# dmesg|fgrep td028
[ 14.530456] panel-tpo-td028ttec1 spi4.0: spi->mode = 00000003
[ 14.599212] panel-tpo-td028ttec1 spi4.0: gpiod disable
[ 14.817871] panel-tpo-td028ttec1 spi4.0: spi->mode = 00000003
[ 14.817871] panel-tpo-td028ttec1 spi4.0: gpiod enable

So it is disabled first and then enabled. Which appears to be the opposite
of what it should be.

BTW: I have added another dev_err to print the spi->mode and like
you describe it is (overwritten? by SPI_MODE_3.

I can check what value it has in the driver before it is set to SPI_MODE_3.

Maybe, there the spi-cs-high gets lost?

BR and thanks,
Nikolaus


> 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.

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