drm/mipi-dsi: Fix theoretical int overflow in mipi_dsi_dcs_write_seq()

The mipi_dsi_dcs_write_seq() macro makes a call to
mipi_dsi_dcs_write_buffer() which returns a type ssize_t. The macro
then stores it in an int and checks to see if it's negative. This
could theoretically be a problem if "ssize_t" is larger than "int".

To see the issue, imagine that "ssize_t" is 32-bits and "int" is
16-bits, you could see a problem if there was some code out there that
looked like:

  mipi_dsi_dcs_write_seq(dsi, cmd, <32767 bytes as arguments>);

...since we'd get back that 32768 bytes were transferred and 32768
stored in a 16-bit int would look negative.

Though there are no callsites where we'd actually hit this (even if
"int" was only 16-bit), it's cleaner to make the types match so let's
fix it.

Fixes: 2a9e9daf7523 ("drm/mipi-dsi: Introduce mipi_dsi_dcs_write_seq macro")
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20240514102056.v5.1.I30fa4c8348ea316c886ef8a522a52fed617f930d@changeid
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240514102056.v5.1.I30fa4c8348ea316c886ef8a522a52fed617f930d@changeid

diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
index 82b1cc434ea3fbede3bb8e878e5a8919a3a3e951..70ce0b8cbc68efe38671808fe45bc1d5fb2eb397 100644 (file)
--- a/include/drm/drm_mipi_dsi.h
+++ b/include/drm/drm_mipi_dsi.h
@@ -333,18 +333,18 @@ int mipi_dsi_dcs_get_display_brightness_large(struct mipi_dsi_device *dsi,
  * @cmd: Command
  * @seq: buffer containing data to be transmitted
  */
-#define mipi_dsi_dcs_write_seq(dsi, cmd, seq...)                           \
-       do {                                                               \
-               static const u8 d[] = { cmd, seq };                        \
-               struct device *dev = &dsi->dev;                            \
-               int ret;                                                   \
-               ret = mipi_dsi_dcs_write_buffer(dsi, d, ARRAY_SIZE(d));    \
-               if (ret < 0) {                                             \
-                       dev_err_ratelimited(                               \
-                               dev, "sending command %#02x failed: %d\n", \
-                               cmd, ret);                                 \
-                       return ret;                                        \
-               }                                                          \
+#define mipi_dsi_dcs_write_seq(dsi, cmd, seq...)                            \
+       do {                                                                \
+               static const u8 d[] = { cmd, seq };                         \
+               struct device *dev = &dsi->dev;                             \
+               ssize_t ret;                                                \
+               ret = mipi_dsi_dcs_write_buffer(dsi, d, ARRAY_SIZE(d));     \
+               if (ret < 0) {                                              \
+                       dev_err_ratelimited(                                \
+                               dev, "sending command %#02x failed: %zd\n", \
+                               cmd, ret);                                  \
+                       return ret;                                         \
+               }                                                           \
        } while (0)
 
 /**