Re: [PATCH] Input: ads7846 - add dummy command register clearing cycle

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Sun, Jun 23, 2024 at 08:21:00PM +0200, Marek Vasut wrote:
> On 3/20/24 8:23 AM, Marek Vasut wrote:
> > On STM32MP135F with XPT2046 touch controller attached to SPI bus, it has
> > been observed that the touch controller locks up after Linux kernel has
> > finished booting. Adding a dummy cycle on the SPI bus seems to mitigate
> > the lock up.
> > 
> > The XPTEK XPT2046 controller seems to be an identical clone of TI TSC2046,
> > the datasheet seems to be a clone of the TI part as well, text seem to be
> > word to word identical, except all the pictures have been drawn again.
> > 
> > This touch controller is present e.g. on WaveShare 3.2inch RPi LCD (B)
> > panel, the DTO provided by WaveShare uses 50 kHz SPI clock for this
> > touch controller, which is unusually low and possibly might have been
> > used as some sort of workaround for an issue. The SPI LCD on the same
> > bus uses 16 MHz clock.
> > 
> > SPI bus DT properties spi-cs-setup-delay-ns, spi-cs-hold-delay-ns,
> > spi-cs-inactive-delay-ns, spi-rx-delay-us, spi-tx-delay-us set to
> > range of 500ns..5us seem to have no impact on the behavior of the
> > touch controller, the lock up always occurs. The STM32MP13xx SPI
> > controller users GPIO control for the nCS pins.
> > 
> > Since the dummy cycle happens after the controller has been put into
> > power down mode and both ADC and REF regulators have been disabled,
> > the cycle should have no impact on the configuration of the controller,
> > i.e. it should be a NOP.
> > 
> > It is unclear whether this problem is specific to this cloned XPT2046
> > controller, or whether this is also present on TSC2046. A test on
> > either TSC2046 or ADS7846 would be very welcome.
> 
> Hi,
> 
> Are there still any open topics with this patch ?

I am concerned that we are putting workaroud for a single controller
into common function. Can we quirk it based on compatible? If not then I
would like someone to run tests on other controllers. Unfortunately I do
not have such hardware.

Linus, do you have devices with ads7846 or tsc2046 by chance? Spitz?

Thanks.

-- 
Dmitry