drm/mipi-dsi: Reduce driver bloat of mipi_dsi_*_write_seq()

Through a cooperative effort between Hsin-Yi Wang and Dmitry
Baryshkov, we have realized the dev_err() in the
mipi_dsi_*_write_seq() macros was causing quite a bit of bloat to the
kernel. Let's hoist this call into drm_mipi_dsi.c by adding a "chatty"
version of the functions that includes the print. While doing this,
add a bit more comments to these macros making it clear that they
print errors and also that they return out of _the caller's_ function.

Without any changes to clients this gives a nice savings. Specifically
the macro was inlined and thus the error report call was inlined into
every call to mipi_dsi_dcs_write_seq() and
mipi_dsi_generic_write_seq(). By using a call to a "chatty" function,
the usage is reduced to one call in the chatty function and a function
call at the invoking site.

Building with my build system shows one example:

$ scripts/bloat-o-meter \
  .../before/panel-novatek-nt36672e.ko \
  .../after/panel-novatek-nt36672e.ko
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-4404 (-4404)
Function                                     old     new   delta
nt36672e_1080x2408_60hz_init               10640    6236   -4404
Total: Before=15055, After=10651, chg -29.25%

Note that given the change in location of the print it's harder to
include the "cmd" in the printout for mipi_dsi_dcs_write_seq() since,
theoretically, someone could call the new chatty function with a
zero-size array and it would be illegal to dereference data[0].
There's a printk format to print the whole buffer and this is probably
more useful for debugging anyway. Given that we're doing this for
mipi_dsi_dcs_write_seq(), let's also print the buffer for
mipi_dsi_generic_write_seq() in the error case.

It should be noted that the current consensus of DRM folks is that the
mipi_dsi_*_write_seq() should be deprecated due to the non-intuitive
return behavior. A future patch will formally mark them as deprecated
and provide an alternative.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
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.v5.4.Id15fae80582bc74a0d4f1338987fa375738f45b9@changeid
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240514102056.v5.4.Id15fae80582bc74a0d4f1338987fa375738f45b9@changeid

2 files changed, 82 insertions, 21 deletions

diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
index 795001bb7ff1..4d2685d5a6e0 100644
--- a/drivers/gpu/drm/drm_mipi_dsi.c
+++ b/drivers/gpu/drm/drm_mipi_dsi.c
@@ -765,6 +765,34 @@ ssize_t mipi_dsi_generic_write(struct mipi_dsi_device *dsi, const void *payload,
 EXPORT_SYMBOL(mipi_dsi_generic_write);
 
 /**
+ * mipi_dsi_generic_write_chatty() - mipi_dsi_generic_write() w/ an error log
+ * @dsi: DSI peripheral device
+ * @payload: buffer containing the payload
+ * @size: size of payload buffer
+ *
+ * Like mipi_dsi_generic_write() but includes a dev_err()
+ * call for you and returns 0 upon success, not the number of bytes sent.
+ *
+ * Return: 0 on success or a negative error code on failure.
+ */
+int mipi_dsi_generic_write_chatty(struct mipi_dsi_device *dsi,
+				  const void *payload, size_t size)
+{
+	struct device *dev = &dsi->dev;
+	ssize_t ret;
+
+	ret = mipi_dsi_generic_write(dsi, payload, size);
+	if (ret < 0) {
+		dev_err(dev, "sending generic data %*ph failed: %zd\n",
+			(int)size, payload, ret);
+		return ret;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(mipi_dsi_generic_write_chatty);
+
+/**
  * mipi_dsi_generic_read() - receive data using a generic read packet
  * @dsi: DSI peripheral device
  * @params: buffer containing the request parameters
@@ -853,6 +881,34 @@ ssize_t mipi_dsi_dcs_write_buffer(struct mipi_dsi_device *dsi,
 EXPORT_SYMBOL(mipi_dsi_dcs_write_buffer);
 
 /**
+ * mipi_dsi_dcs_write_buffer_chatty - mipi_dsi_dcs_write_buffer() w/ an error log
+ * @dsi: DSI peripheral device
+ * @data: buffer containing data to be transmitted
+ * @len: size of transmission buffer
+ *
+ * Like mipi_dsi_dcs_write_buffer() but includes a dev_err()
+ * call for you and returns 0 upon success, not the number of bytes sent.
+ *
+ * Return: 0 on success or a negative error code on failure.
+ */
+int mipi_dsi_dcs_write_buffer_chatty(struct mipi_dsi_device *dsi,
+				     const void *data, size_t len)
+{
+	struct device *dev = &dsi->dev;
+	ssize_t ret;
+
+	ret = mipi_dsi_dcs_write_buffer(dsi, data, len);
+	if (ret < 0) {
+		dev_err(dev, "sending dcs data %*ph failed: %zd\n",
+			(int)len, data, ret);
+		return ret;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(mipi_dsi_dcs_write_buffer_chatty);
+
+/**
  * mipi_dsi_dcs_write() - send DCS write command
  * @dsi: DSI peripheral device
  * @cmd: DCS command
diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
index 67967be48dbd..6d68d9927f46 100644
--- a/include/drm/drm_mipi_dsi.h
+++ b/include/drm/drm_mipi_dsi.h
@@ -256,6 +256,8 @@ int mipi_dsi_picture_parameter_set(struct mipi_dsi_device *dsi,
 
 ssize_t mipi_dsi_generic_write(struct mipi_dsi_device *dsi, const void *payload,
 			       size_t size);
+int mipi_dsi_generic_write_chatty(struct mipi_dsi_device *dsi,
+				  const void *payload, size_t size);
 ssize_t mipi_dsi_generic_read(struct mipi_dsi_device *dsi, const void *params,
 			      size_t num_params, void *data, size_t size);
 
@@ -279,6 +281,8 @@ enum mipi_dsi_dcs_tear_mode {
 
 ssize_t mipi_dsi_dcs_write_buffer(struct mipi_dsi_device *dsi,
 				  const void *data, size_t len);
+int mipi_dsi_dcs_write_buffer_chatty(struct mipi_dsi_device *dsi,
+				     const void *data, size_t len);
 ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, u8 cmd,
 			   const void *data, size_t len);
 ssize_t mipi_dsi_dcs_read(struct mipi_dsi_device *dsi, u8 cmd, void *data,
@@ -311,38 +315,39 @@ int mipi_dsi_dcs_get_display_brightness_large(struct mipi_dsi_device *dsi,
 
 /**
  * mipi_dsi_generic_write_seq - transmit data using a generic write packet
+ *
+ * This macro will print errors for you and will RETURN FROM THE CALLING
+ * FUNCTION (yes this is non-intuitive) upon error.
+ *
  * @dsi: DSI peripheral device
  * @seq: buffer containing the payload
  */
-#define mipi_dsi_generic_write_seq(dsi, seq...)                           \
-	do {                                                              \
-		static const u8 d[] = { seq };                            \
-		struct device *dev = &dsi->dev;                           \
-		ssize_t ret;                                              \
-		ret = mipi_dsi_generic_write(dsi, d, ARRAY_SIZE(d));      \
-		if (ret < 0) {                                            \
-			dev_err(dev, "transmit data failed: %zd\n", ret); \
-			return ret;                                       \
-		}                                                         \
+#define mipi_dsi_generic_write_seq(dsi, seq...)                                \
+	do {                                                                   \
+		static const u8 d[] = { seq };                                 \
+		int ret;                                                       \
+		ret = mipi_dsi_generic_write_chatty(dsi, d, ARRAY_SIZE(d));    \
+		if (ret < 0)                                                   \
+			return ret;                                            \
 	} while (0)
 
 /**
  * mipi_dsi_dcs_write_seq - transmit a DCS command with payload
+ *
+ * This macro will print errors for you and will RETURN FROM THE CALLING
+ * FUNCTION (yes this is non-intuitive) upon error.
+ *
  * @dsi: DSI peripheral device
  * @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;                             \
-		ssize_t ret;                                                \
-		ret = mipi_dsi_dcs_write_buffer(dsi, d, ARRAY_SIZE(d));     \
-		if (ret < 0) {                                              \
-			dev_err(dev, "sending command %#02x failed: %zd\n", \
-				cmd, ret);                                  \
-			return ret;                                         \
-		}                                                           \
+#define mipi_dsi_dcs_write_seq(dsi, cmd, seq...)                               \
+	do {                                                                   \
+		static const u8 d[] = { cmd, seq };                            \
+		int ret;                                                       \
+		ret = mipi_dsi_dcs_write_buffer_chatty(dsi, d, ARRAY_SIZE(d)); \
+		if (ret < 0)                                                   \
+			return ret;                                            \
 	} while (0)
 
 /**