[PATCH v2] drm/dbi: Print errors for mipi_dbi_command()

[Noralf Trønnes]

Den 02.07.2021 12.04, skrev Linus Walleij:
> The macro mipi_dbi_command() does not report errors unless you wrap it
> in another macro to do the error reporting.
> 
> Report a rate-limited error so we know what is going on.
> 
> Drop the only user in DRM using mipi_dbi_command() and actually checking
> the error explicitly, let it use mipi_dbi_command_buf() directly
> instead.
> 
> After this any code wishing to send command arrays can rely on
> mipi_dbi_command() providing an appropriate error message if something
> goes wrong.
> 
> Suggested-by: Noralf Trønnes <noralf at tronnes.org>
> Suggested-by: Douglas Anderson <dianders at chromium.org>
> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
> ---
> ChangeLog v1->v2:
> - Fish out the struct device * from the DBI SPI client and use
>   that to print the errors associated with the SPI device.
> ---
>  drivers/gpu/drm/drm_mipi_dbi.c | 2 +-
>  include/drm/drm_mipi_dbi.h     | 6 +++++-
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
> index 3854fb9798e9..c7c1b75df190 100644
> --- a/drivers/gpu/drm/drm_mipi_dbi.c
> +++ b/drivers/gpu/drm/drm_mipi_dbi.c
> @@ -645,7 +645,7 @@ static int mipi_dbi_poweron_reset_conditional(struct mipi_dbi_dev *dbidev, bool
>  		return 1;
>  
>  	mipi_dbi_hw_reset(dbi);
> -	ret = mipi_dbi_command(dbi, MIPI_DCS_SOFT_RESET);
> +	ret = mipi_dbi_command_buf(dbi, MIPI_DCS_SOFT_RESET, NULL, 0);
>  	if (ret) {
>  		DRM_DEV_ERROR(dev, "Failed to send reset command (%d)\n", ret);
>  		if (dbidev->regulator)
> diff --git a/include/drm/drm_mipi_dbi.h b/include/drm/drm_mipi_dbi.h
> index f543d6e3e822..f00cb9690cf2 100644
> --- a/include/drm/drm_mipi_dbi.h
> +++ b/include/drm/drm_mipi_dbi.h
> @@ -183,7 +183,11 @@ int mipi_dbi_buf_copy(void *dst, struct drm_framebuffer *fb,
>  #define mipi_dbi_command(dbi, cmd, seq...) \
>  ({ \
>  	const u8 d[] = { seq }; \
> -	mipi_dbi_command_stackbuf(dbi, cmd, d, ARRAY_SIZE(d)); \
> +	struct device *dev = &dbi->spi->dev; \
> +	int ret; \
> +	ret = mipi_dbi_command_stackbuf(dbi, cmd, d, ARRAY_SIZE(d)); \
> +	if (ret) \
> +		dev_err_ratelimited(dev, "error %d when sending command\n", ret); \

Nit: Printing the failing command would have been useful, like you did
in the driver macro.

>  })

I would have preferred if mipi_dbi_command could have returned the error
code. This indicates that it should be possible:
https://stackoverflow.com/questions/3532621/using-and-returning-output-in-c-macro

But I can live with this, but if drivers want to start checking the
error code we might have to rethink this.

But this works as things are now:

Reviewed-by: Noralf Trønnes <noralf at tronnes.org>