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From: Douglas Anderson <dianders@chromium.org>
To: dri-devel@lists.freedesktop.org
Cc: Linus Walleij <linus.walleij@linaro.org>,
	lvzhaoxiong@huaqin.corp-partner.google.com,
	Jani Nikula <jani.nikula@linux.intel.com>,
	Hsin-Yi Wang <hsinyi@google.com>,
	Javier Martinez Canillas <javierm@redhat.com>,
	Neil Armstrong <neil.armstrong@linaro.org>,
	Joel Selvaraj <jo@jsfamily.in>,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	Cong Yang <yangcong5@huaqin.corp-partner.google.com>,
	Sam Ravnborg <sam@ravnborg.org>,
	Douglas Anderson <dianders@chromium.org>,
	Daniel Vetter <daniel@ffwll.ch>,
	David Airlie <airlied@gmail.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2 3/8] drm/mipi-dsi: Reduce driver bloat of mipi_dsi_*_write_seq()
Date: Fri, 26 Apr 2024 16:58:36 -0700
Message-ID: <20240426165839.v2.3.Id15fae80582bc74a0d4f1338987fa375738f45b9@changeid>
In-Reply-To: <20240426235857.3870424-1-dianders@chromium.org>
References: <20240426235857.3870424-1-dianders@chromium.org>
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Through a cooperative effort between Hsin-Yi Wang and Dmitry
Baryshkov, we have realized the dev_err_ratelimited() 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 dramatic savings. Building
with my build system shows one example:

$ scripts/bloat-o-meter \
  .../before/panel-novatek-nt36672e.ko \
  .../after/panel-novatek-nt36672e.ko

add/remove: 0/1 grow/shrink: 0/1 up/down: 0/-21496 (-21496)
Function                                     old     new   delta
nt36672e_1080x2408_60hz_init._rs           10320       -  -10320
nt36672e_1080x2408_60hz_init               17412    6236  -11176
Total: Before=32147, After=10651, chg -66.87%

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.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

Changes in v2:
- Add some comments to the macros about printing and returning.
- Modify commit message now that this is part of a series.
- Change the way err value is handled in prep for next patch.
- Rebased upon patches to avoid theoretical int overflow.

 drivers/gpu/drm/drm_mipi_dsi.c | 56 ++++++++++++++++++++++++++++++++++
 include/drm/drm_mipi_dsi.h     | 41 +++++++++++++------------
 2 files changed, 78 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
index 795001bb7ff1..1e062eda3b88 100644
--- a/drivers/gpu/drm/drm_mipi_dsi.c
+++ b/drivers/gpu/drm/drm_mipi_dsi.c
@@ -764,6 +764,34 @@ 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_ratelimited()
+ * 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_ratelimited(dev, "sending generic data %*ph failed: %d\n",
+				    (int)size, payload, (int)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
@@ -852,6 +880,34 @@ 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_ratelimited()
+ * 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_ratelimited(dev, "sending dcs data %*ph failed: %d\n",
+				    (int)len, data, (int)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
diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
index 5de2bd62448b..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,
@@ -311,40 +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_ratelimited(dev, "transmit data failed: %d\n", \
-					    (int)ret);                         \
+		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_ratelimited(                               \
-				dev, "sending command %#02x failed: %d\n", \
-				cmd, (int)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)
 
 /**
-- 
2.44.0.769.g3c40516874-goog