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Message-ID: <f52a8452-4219-4b25-9cf5-2ae6c8747ac8@linaro.org>
Date: Thu, 2 May 2024 09:27:46 +0200
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From: Neil Armstrong <neil.armstrong@linaro.org>
Reply-To: neil.armstrong@linaro.org
Subject: Re: [PATCH v3 4/9] drm/mipi-dsi: Reduce driver bloat of
 mipi_dsi_*_write_seq()
To: Douglas Anderson <dianders@chromium.org>, dri-devel@lists.freedesktop.org
Cc: Linus Walleij <linus.walleij@linaro.org>,
 Jani Nikula <jani.nikula@linux.intel.com>,
 Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
 Cong Yang <yangcong5@huaqin.corp-partner.google.com>,
 Hsin-Yi Wang <hsinyi@google.com>, Brian Norris <briannorris@chromium.org>,
 Sam Ravnborg <sam@ravnborg.org>,
 Javier Martinez Canillas <javierm@redhat.com>, Joel Selvaraj
 <jo@jsfamily.in>, lvzhaoxiong@huaqin.corp-partner.google.com,
 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
References: <20240501154251.3302887-1-dianders@chromium.org>
 <20240501084109.v3.4.Id15fae80582bc74a0d4f1338987fa375738f45b9@changeid>
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On 01/05/2024 17:41, Douglas Anderson wrote:
> 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. 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>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
> Changes in v3:
> - Rebased upon patch to remove ratelimit of prints.
> 
> Changes in v2:
> - Add some comments to the macros about printing and returning.
> - Change the way err value is handled in prep for next patch.
> - Modify commit message now that this is part of a series.
> - Rebased upon patches to avoid theoretical int overflow.
> 
>   drivers/gpu/drm/drm_mipi_dsi.c | 56 ++++++++++++++++++++++++++++++++++
>   include/drm/drm_mipi_dsi.h     | 47 +++++++++++++++-------------
>   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..8593d9ed5891 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(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
> @@ -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(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
> 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)
>   
>   /**

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>