linux-kernel - Re: [PATCH RFC v2 17/18] drm/vkms: Introduce config for connector EDID

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Message-ID: <87o723y7dr.fsf@intel.com>
Date: Mon, 25 Nov 2024 11:45:04 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Louis Chauvet <louis.chauvet@...tlin.com>, Maíra Canal
 <mairacanal@...eup.net>, Haneen Mohammed <hamohammed.sa@...il.com>, Simona
 Vetter <simona@...ll.ch>, Melissa Wen <melissa.srw@...il.com>, Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David
 Airlie <airlied@...il.com>
Cc: arthurgrillo@...eup.net, jeremie.dautheribes@...tlin.com,
 miquel.raynal@...tlin.com, thomas.petazzoni@...tlin.com,
 seanpaul@...gle.com, nicolejadeyee@...gle.com,
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, Louis
 Chauvet <louis.chauvet@...tlin.com>
Subject: Re: [PATCH RFC v2 17/18] drm/vkms: Introduce config for connector EDID

On Fri, 22 Nov 2024, Louis Chauvet <louis.chauvet@...tlin.com> wrote:
> To properly test the EDID reading without using the DRM override, add an
> option to configure the EDID for a connector.
>
> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> ---
>  drivers/gpu/drm/vkms/vkms_config.c |  1 +
>  drivers/gpu/drm/vkms/vkms_config.h |  2 ++
>  drivers/gpu/drm/vkms/vkms_output.c | 37 ++++++++++++++++++++++++++++++++++---
>  3 files changed, 37 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/vkms/vkms_config.c b/drivers/gpu/drm/vkms/vkms_config.c
> index ac1a9658c5075c118d59da965ca3392355ccb2b2..1a1234d4f10fa8e5ea6bd649139ecc10c991f875 100644
> --- a/drivers/gpu/drm/vkms/vkms_config.c
> +++ b/drivers/gpu/drm/vkms/vkms_config.c
> @@ -199,6 +199,7 @@ struct vkms_config_connector *vkms_config_create_connector(struct vkms_config *v
>  	xa_init_flags(&vkms_config_connector->possible_encoders, XA_FLAGS_ALLOC);
>  	vkms_config_connector->type = DRM_MODE_CONNECTOR_VIRTUAL;
>  	vkms_config_connector->status = connector_status_unknown;
> +	vkms_config_connector->edid_blob_len = 0;
>  
>  	return vkms_config_connector;
>  }
> diff --git a/drivers/gpu/drm/vkms/vkms_config.h b/drivers/gpu/drm/vkms/vkms_config.h
> index bba56c9d8aeceac97a4339ef42ab663c5dc54e65..1220b16f6c98d1ebb0ae55d662a84fe25e1a6a02 100644
> --- a/drivers/gpu/drm/vkms/vkms_config.h
> +++ b/drivers/gpu/drm/vkms/vkms_config.h
> @@ -112,6 +112,8 @@ struct vkms_config_connector {
>  	struct xarray possible_encoders;
>  	int type;
>  	enum drm_connector_status status;
> +	char edid_blob[PAGE_SIZE];
> +	int edid_blob_len;
>  
>  	/* Internal usage */
>  	struct drm_connector *connector;
> diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
> index fc6a0cdade0739b94820ed4e0924cf355137fe79..56590afb33d75465971d10a282040690840cdbee 100644
> --- a/drivers/gpu/drm/vkms/vkms_output.c
> +++ b/drivers/gpu/drm/vkms/vkms_output.c
> @@ -31,13 +31,44 @@ static const struct drm_connector_funcs vkms_connector_funcs = {
>  	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
>  };
>  
> +static int vkms_connector_read_block(void *context, u8 *buf, unsigned int block, size_t len)
> +{
> +	struct vkms_config_connector *config = context;
> +
> +	if (block * len + len > config->edid_blob_len)

The parameters to the read block function are a bit weird for historical
reasons. The start offset is indicated by block number, length by
len. The start byte offset is thus block * EDID_LENGTH! There's no
smaller granularity for start offset. However len can be < EDID_LENGTH!

So the above should be (block * EDID_LENGTH + len > edid_blob_len)

> +		return 1;
> +	memcpy(buf, &config->edid_blob[block * len], len);

And this should be &config->edid_blob[block * EDID_LENGTH].

(Your patch would work, but just by coincidence due to the way the read
block function is currently called.)

> +	return 0;
> +}
> +
>  static int vkms_conn_get_modes(struct drm_connector *connector)
>  {
> +	const struct drm_edid *drm_edid = NULL;
>  	int count;
> +	struct vkms_config_connector *connector_cfg;
> +	struct vkms_device *vkmsdev = drm_device_to_vkms_device(connector->dev);
> +	struct vkms_config_connector *context = NULL;
> +
> +	list_for_each_entry(connector_cfg, &vkmsdev->config->connectors, link) {
> +		if (connector_cfg->connector == connector) {
> +			context = connector_cfg;
> +			break;
> +		}
> +	}
> +	if (context)
> +		drm_edid = drm_edid_read_custom(connector, vkms_connector_read_block, context);

Thanks for using drm_edid_read_custom() for this btw!

> +
> +	/*
> +	 * Unconditionally update the connector. If the EDID was read
> +	 * successfully, fill in the connector information derived from the
> +	 * EDID. Otherwise, if the EDID is NULL, clear the connector
> +	 * information.
> +	 */
> +	drm_edid_connector_update(connector, drm_edid);
> +
> +	count = drm_edid_connector_add_modes(connector);
>  
> -	/* Use the default modes list from DRM */
> -	count = drm_add_modes_noedid(connector, XRES_MAX, YRES_MAX);
> -	drm_set_preferred_mode(connector, XRES_DEF, YRES_DEF);

I don't really know anything about your use case, but don't you want to
fall back to the above for drm_edid == NULL? *shrug*

BR,
Jani.

> +	drm_edid_free(drm_edid);
>  
>  	return count;
>  }

-- 
Jani Nikula, Intel