linux-kernel - Re: [PATCH 2/3] drm/mipi-dsi: add mipi_dsi_compression_mode

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Message-ID: <cmevrewvs4ultfn5yeo2yqxt3eo7kpw2bt4sgeoirv7k5oske5@qv2niojixnuy>
Date: Mon, 1 Apr 2024 12:38:17 +0200
From: Marijn Suijten <marijn.suijten@...ainline.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Sumit Semwal <sumit.semwal@...aro.org>, 
	Caleb Connolly <caleb.connolly@...aro.org>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Jessica Zhang <quic_jesszhan@...cinc.com>, Sam Ravnborg <sam@...nborg.org>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH 2/3] drm/mipi-dsi: add mipi_dsi_compression_mode_raw()

On 2024-03-30 05:59:29, Dmitry Baryshkov wrote:
> The LG SW43408 panel requires sending non-standard data as a part of the
> MIPI_DSI_COMPRESSION_MODE packet. Rather than hacking existing
> mipi_dsi_compression_mode() add mipi_dsi_compression_mode_raw(), which
> accepts raw data buffer and length.

Even though I doubt the usefulness of this _raw() command before further
understanding the panel and driver (according the the review-followup sent a few
minutes ago), let me review this a little bit.

> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> ---
>  drivers/gpu/drm/drm_mipi_dsi.c | 34 ++++++++++++++++++++++++++--------
>  include/drm/drm_mipi_dsi.h     |  1 +
>  2 files changed, 27 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
> index ef6e416522f8..f340d1e0a9a5 100644
> --- a/drivers/gpu/drm/drm_mipi_dsi.c
> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
> @@ -645,29 +645,47 @@ int mipi_dsi_set_maximum_return_packet_size(struct mipi_dsi_device *dsi,
>  EXPORT_SYMBOL(mipi_dsi_set_maximum_return_packet_size);
>  
>  /**
> - * mipi_dsi_compression_mode() - enable/disable DSC on the peripheral
> + * mipi_dsi_compression_mode_raw() - control DSC on the peripheral
>   * @dsi: DSI peripheral device
> - * @enable: Whether to enable or disable the DSC
> + * @data: data to be sent to the device
> + * @len: size of the data buffer
>   *
> - * Enable or disable Display Stream Compression on the peripheral using the
> + * Control the Display Stream Compression on the peripheral using the

+ mode?

>   * default Picture Parameter Set and VESA DSC 1.1 algorithm.

This is no longer true.  Both the algoritm identifier and "default Picture
Parameter Set" (which I assume means table *index*!) are described by the
custom/raw bytes that one is allowed to pass.

In fact, in the SW43408 driver that you reference in the commit message the
custom data passed to the _raw() function is used to select the second PPS
table (unless the panel interprets the input data in a non-standard way...), and
further sets the PPS for the first table only :)

>   *
>   * Return: 0 on success or a negative error code on failure.
>   */
> -ssize_t mipi_dsi_compression_mode(struct mipi_dsi_device *dsi, bool enable)
> +ssize_t mipi_dsi_compression_mode_raw(struct mipi_dsi_device *dsi, void *data, size_t len)
>  {
> -	/* Note: Needs updating for non-default PPS or algorithm */
> -	u8 tx[2] = { enable << 0, 0 };
>  	struct mipi_dsi_msg msg = {
>  		.channel = dsi->channel,
>  		.type = MIPI_DSI_COMPRESSION_MODE,
> -		.tx_len = sizeof(tx),
> -		.tx_buf = tx,
> +		.tx_len = len,
> +		.tx_buf = data,
>  	};
>  	int ret = mipi_dsi_device_transfer(dsi, &msg);
>  
>  	return (ret < 0) ? ret : 0;
>  }
> +EXPORT_SYMBOL(mipi_dsi_compression_mode_raw);
> +
> +/**
> + * mipi_dsi_compression_mode() - enable/disable DSC on the peripheral
> + * @dsi: DSI peripheral device
> + * @enable: Whether to enable or disable the DSC
> + *
> + * Enable or disable Display Stream Compression on the peripheral using the
> + * default Picture Parameter Set and VESA DSC 1.1 algorithm.

And while fixing this up, let's make it clear that this doesn't change the
PPS, just the *index* of which PPS to use (the PPS is updated with a different
command).

- Marijn

> + *
> + * Return: 0 on success or a negative error code on failure.
> + */
> +ssize_t mipi_dsi_compression_mode(struct mipi_dsi_device *dsi, bool enable)
> +{
> +	/* Note: Needs updating for non-default PPS or algorithm */
> +	u8 tx[2] = { enable << 0, 0 };
> +
> +	return mipi_dsi_compression_mode_raw(dsi, tx, sizeof(tx));
> +}
>  EXPORT_SYMBOL(mipi_dsi_compression_mode);
>  
>  /**
> diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
> index c0aec0d4d664..321d2b019687 100644
> --- a/include/drm/drm_mipi_dsi.h
> +++ b/include/drm/drm_mipi_dsi.h
> @@ -242,6 +242,7 @@ int mipi_dsi_turn_on_peripheral(struct mipi_dsi_device *dsi);
>  int mipi_dsi_set_maximum_return_packet_size(struct mipi_dsi_device *dsi,
>  					    u16 value);
>  ssize_t mipi_dsi_compression_mode(struct mipi_dsi_device *dsi, bool enable);
> +ssize_t mipi_dsi_compression_mode_raw(struct mipi_dsi_device *dsi, void *data, size_t len);
>  ssize_t mipi_dsi_picture_parameter_set(struct mipi_dsi_device *dsi,
>  				       const struct drm_dsc_picture_parameter_set *pps);
>  
> 
> -- 
> 2.39.2
>