[PATCH v3] drm/dbi: Print errors for mipi_dbi_command()

[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 v2->v3:
- Make the macro actually return the error value if need be, by
  putting a single ret; at the end of the macro. (Neat trick from
  StackOverflow!)
- Switch the site where I switched mipi_dbi_command() to
  mipi_dbi_command_buf() back to what it was.
- Print the failed command in the error message.
- Put the dbi in (parens) since drivers/gpu/drm/tiny/st7586.c was
  passing &dbidev->dbi as parameter to mipi_dbi_command()
  and this would expand to
  struct device *dev = &&dbidev->dbi->spi->dev
  which can't be parsed but
  struct device *dev = &(&dbidev->dbi)->spi-dev;
  should work. I hope.
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.
---
 include/drm/drm_mipi_dbi.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/drm/drm_mipi_dbi.h b/include/drm/drm_mipi_dbi.h
index f543d6e3e822..05e194958265 100644
--- a/include/drm/drm_mipi_dbi.h
+++ b/include/drm/drm_mipi_dbi.h
@@ -183,7 +183,12 @@ 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 %#02x\n", ret, cmd); \
+	ret; \
 })
 
 #ifdef CONFIG_DEBUG_FS
-- 
2.31.1