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Message-ID: <300eab2e-f884-4978-9f19-b764bb5fb47a@linaro.org>
Date: Thu, 25 Apr 2024 09:55:11 +0200
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Douglas Anderson <dianders@...omium.org>, dri-devel@...ts.freedesktop.org
Cc: Javier Martinez Canillas <javierm@...hat.com>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, linus.walleij@...aro.org,
 Cong Yang <yangcong5@...qin.corp-partner.google.com>,
 lvzhaoxiong@...qin.corp-partner.google.com, Hsin-Yi Wang
 <hsinyi@...gle.com>, Sam Ravnborg <sam@...nborg.org>,
 Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/mipi-dsi: Reduce driver bloat of
 mipi_dsi_*_write_seq()

On 25/04/2024 02:20, Douglas Anderson wrote:
> The consensus of many DRM folks is that we want to move away from DSI
> drivers defining tables of init commands. Instead, we want to move to
> init functions that can use common DRM functions. The issue thus far
> has been that using the macros mipi_dsi_generic_write_seq() and
> mipi_dsi_dcs_write_seq() bloats the driver using them.
> 
> Through a cooperative effort between Hsin-Yi Wang and Dmitry
> Baryshkov, we have realized that the majority of the bloat is the fact
> that we have the dev_err_ratelimited() directly in the macros. Let's
> hoist this call into drm_mipi_dsi.c by adding a "chatty" version of
> the functions that includes the print.
> 
> 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: 1/1 up/down: 6/-19652 (-19646)
> Function                                     old     new   delta
> __UNIQUE_ID_vermagic520                       64      70      +6
> nt36672e_1080x2408_60hz_init               16592    7260   -9332
> nt36672e_1080x2408_60hz_init._rs           10320       -  -10320
> Total: Before=31503, After=11857, chg -62.36%
> 
> 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.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> The MIPI device I have in front of me (wormdingler) hasn't been
> converted to use these functions yet, so this is just compile
> tested. It's about my end of day so I'm sending this out since it's
> pretty straightforward. Hopefully others can confirm it works well for
> them and also saves space under their compilers.
> 
>   drivers/gpu/drm/drm_mipi_dsi.c | 54 ++++++++++++++++++++++++++++++++++
>   include/drm/drm_mipi_dsi.h     | 31 ++++++++-----------
>   2 files changed, 67 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
> index 795001bb7ff1..5ded6aef38ed 100644
> --- a/drivers/gpu/drm/drm_mipi_dsi.c
> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
> @@ -764,6 +764,33 @@ 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
> + *
> + * Just like mipi_dsi_generic_write() but includes a dev_err_ratelimited()
> + * call for you.
> + *
> + * Return: The number of bytes transmitted on success or a negative error code
> + * on failure.
> + */
> +ssize_t mipi_dsi_generic_write_chatty(struct mipi_dsi_device *dsi,
> +				      const void *payload, size_t size)
> +{
> +	struct device *dev = &dsi->dev;
> +	int 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, ret);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(mipi_dsi_generic_write_chatty);
> +
>   /**
>    * mipi_dsi_generic_read() - receive data using a generic read packet
>    * @dsi: DSI peripheral device
> @@ -852,6 +879,33 @@ 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
> + *
> + * Just like mipi_dsi_dcs_write_buffer() but includes a dev_err_ratelimited()
> + * call for you.
> + *
> + * Return: The number of bytes successfully transmitted or a negative error
> + * code on failure.
> + */
> +ssize_t mipi_dsi_dcs_write_buffer_chatty(struct mipi_dsi_device *dsi,
> +					 const void *data, size_t len)
> +{
> +	struct device *dev = &dsi->dev;
> +	int 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, ret);
> +
> +	return ret;
> +}
> +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 82b1cc434ea3..784e425dc4c8 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);
> +ssize_t 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);
> +ssize_t 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,
> @@ -317,14 +321,10 @@ int mipi_dsi_dcs_get_display_brightness_large(struct mipi_dsi_device *dsi,
>   #define mipi_dsi_generic_write_seq(dsi, seq...)                                \
>   	do {                                                                   \
>   		static const u8 d[] = { seq };                                 \
> -		struct device *dev = &dsi->dev;                                \
>   		int ret;                                                       \
> -		ret = mipi_dsi_generic_write(dsi, d, ARRAY_SIZE(d));           \
> -		if (ret < 0) {                                                 \
> -			dev_err_ratelimited(dev, "transmit data failed: %d\n", \
> -					    ret);                              \
> +		ret = mipi_dsi_generic_write_chatty(dsi, d, ARRAY_SIZE(d));    \
> +		if (ret < 0)                                                   \
>   			return ret;                                            \
> -		}                                                              \
>   	} while (0)
>   
>   /**
> @@ -333,18 +333,13 @@ 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 };                            \
> +		int ret;                                                       \
> +		ret = mipi_dsi_dcs_write_buffer_chatty(dsi, d, ARRAY_SIZE(d)); \
> +		if (ret < 0)                                                   \
> +			return ret;                                            \
>   	} while (0)
>   
>   /**

At first sight it looks o for me, it's less efficient since it adds a function call
for each sequence, but the saving if very significant.

I'll run a test on the vtdr6130 to be sure.

Neil

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