Re: [PATCH] spi: bcm2835: Convert to use CS GPIO descriptors

[kernel@xxxxxxxxxxxxxxxx]

Hi Linus!


> On 20.04.2019, at 13:08, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> 
> This converts the BCM2835 SPI master driver to use GPIO
> descriptors for chip select handling.
> 
> The BCM2835 driver was relying on the core to drive the
> CS high/low so very small changes were needed for this
> part. If it managed to request the CS from the device tree
> node, all is pretty straight forward.
> 
> However for native GPIOs this driver has a quite unorthodox
> loopback to request some GPIOs from the SoC GPIO chip by
> looking it up from the device tree using gpiochip_find()
> and then offseting hard into its numberspace. This has
> been augmented a bit by using gpiochip_request_own_desc()
> but this code really needs to be verified. If "native CS"
> is actually an SoC GPIO, why is it even done this way?
> Should this GPIO not just be defined in the device tree
> like any other CS GPIO? I'm confused.
> 
> Cc: Lukas Wunner <lukas@xxxxxxxxx>
> Cc: Stefan Wahren <stefan.wahren@xxxxxxxx>
> Cc: Martin Sperl <kernel@xxxxxxxxxxxxxxxx>
> Cc: Chris Boot <bootc@xxxxxxxxx>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
> ChangeLog RFT->v2:
> - Rebased on v5.1-rc1
> 
> I would very much appreciate if someone took this for
> a ride on top of linux-next (there are some fixes in
> the -rcs you need) and see if all still works as expected.


Just applying this single patch gives me:
  CC [M]  drivers/spi/spi-bcm2835.o
drivers/spi/spi-bcm2835.c: In function ‘bcm2835_spi_setup’:
drivers/spi/spi-bcm2835.c:883:6: warning: unused variable ‘err’ [-Wunused-variable]
  int err;
      ^~~

Then loading the module:
[   30.403459] spi spi0.0: FIXME: setting up native-CS0 as GPIO

But when loading a spi-device driver it does not detect the device.

One note: the logic analyzer shows that the CS line is inverted
(high on SPI Clock running)

With the un-patched version I get the following in dmesg:
root@raspcm3:~# dmesg
[   27.987287] spi spi0.0: setting up native-CS0 as GPIO 2002

So you see that I am using the “original” DT that relies on the
translation to gpio by the driver.

Martin