Re: [PATCH v3 2/4] drm/edid: Add a function to check monitor string

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 04 Mar 2024, Hsin-Yi Wang <hsinyi@chromium.org> wrote:
> Add a function to check if the EDID base block contains a given string.
>
> One of the use cases is fetching panel from a list of panel names, since
> some panel vendors put the monitor name after EDID_DETAIL_MONITOR_STRING
> instead of EDID_DETAIL_MONITOR_NAME.
>
> Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
> ---
> v2->v3: move string matching to drm_edid
> ---
>  drivers/gpu/drm/drm_edid.c | 49 ++++++++++++++++++++++++++++++++++++++
>  include/drm/drm_edid.h     |  1 +
>  2 files changed, 50 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 13454bc64ca2..fcdc2bd143dd 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -2789,6 +2789,55 @@ u32 drm_edid_get_panel_id(struct edid_base_block *base_block)
>  }
>  EXPORT_SYMBOL(drm_edid_get_panel_id);
>  
> +/**
> + * drm_edid_has_monitor_string - Check if a EDID base block has certain string.
> + * @base_block: EDID base block to check.
> + * @str: pointer to a character array to hold the string to be checked.
> + *
> + * Check if the detailed timings section of a EDID base block has the given
> + * string.
> + *
> + * Return: True if the EDID base block contains the string, false otherwise.
> + */
> +bool drm_edid_has_monitor_string(struct edid_base_block *base_block, const char *str)
> +{
> +	unsigned int i, j, k, buflen = strlen(str);
> +
> +	for (i = 0; i < EDID_DETAILED_TIMINGS; i++) {
> +		struct detailed_timing *timing = &base_block->edid.detailed_timings[i];
> +		unsigned int size = ARRAY_SIZE(timing->data.other_data.data.str.str);
> +
> +		if (buflen > size || timing->pixel_clock != 0 ||
> +		    timing->data.other_data.pad1 != 0 ||
> +		    (timing->data.other_data.type != EDID_DETAIL_MONITOR_NAME &&
> +		     timing->data.other_data.type != EDID_DETAIL_MONITOR_STRING))
> +			continue;
> +
> +		for (j = 0; j < buflen; j++) {
> +			char c = timing->data.other_data.data.str.str[j];
> +
> +			if (c != str[j] ||  c == '\n')
> +				break;
> +		}
> +
> +		if (j == buflen) {
> +			/* Allow trailing white spaces. */
> +			for (k = j; k < size; k++) {
> +				char c = timing->data.other_data.data.str.str[k];
> +
> +				if (c == '\n')
> +					return true;
> +				else if (c != ' ')
> +					break;
> +			}
> +			if (k == size)
> +				return true;
> +		}
> +	}
> +
> +	return false;
> +}
> +

So we've put a lot of effort into converting from struct edid to struct
drm_edid, passing that around in drm_edid.c, with the allocation size it
provides, and generally cleaning stuff up.

I'm not at all happy to see *another* struct added just for the base
block, and detailed timing iteration as well as monitor name parsing
duplicated.

With struct drm_edid you can actually return an EDID that only has the
base block and size 128, even if the EDID indicates more
extensions. Because the whole thing is *designed* to handle that
gracefully. The allocated size matters, not what the blob originating
outside of the kernel tells you.

What I'm thinking is:

- Add some struct drm_edid_ident or similar. Add all the information
  that's needed to identify a panel there. I guess initially that's
  panel_id and name.

    struct drm_edid_ident {
        u32 panel_id;
        const char *name;
    };

- Add function:

    bool drm_edid_match(const struct drm_edid *drm_edid, const struct drm_edid_ident *ident);

  Check if stuff in ident matches drm_edid. You can use and extend the
  existing drm_edid based iteration etc. in
  drm_edid.c. Straightforward. The fields in ident can trivially be
  extended later, and the stuff can be useful for other drivers and
  quirks etc.

- Restructure struct edp_panel_entry to contain struct
  drm_edid_ident. Change the iteration of edp_panels array to use
  drm_edid_match() on the array elements and the edid.

- Add a function to read the EDID base block *but* make it return const
  struct drm_edid *. Add warnings in the comments that it's only for
  panel and for transition until it switches to reading full EDIDs.

    const struct drm_edid *drm_edid_read_base_block(struct i2c_adapter *adapter);

  This is the *only* hackish part of the whole thing, and it's nicely
  isolated. For the most part you can use drm_edid_get_panel_id() code
  for this, just return the blob wrapped in a struct drm_edid envelope.

- Remove function:

    u32 drm_edid_get_panel_id(struct i2c_adapter *adapter);

- Refactor edid_quirk_list to use the same id struct and match function
  and mechanism within drm_edid.c (can be follow-up too).

- Once you change the panel code to read the whole EDID using
  drm_edid_read family of functions in the future, you don't have to
  change *anything* about the iteration or matching or anything, because
  it's already passing struct drm_edid around.


I hope this covers everything.

BR,
Jani.


>  /**
>   * drm_edid_get_base_block - Get a panel's EDID base block
>   * @adapter: I2C adapter to use for DDC
> diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
> index 2455d6ab2221..248ddb0a6b5d 100644
> --- a/include/drm/drm_edid.h
> +++ b/include/drm/drm_edid.h
> @@ -416,6 +416,7 @@ struct edid *drm_get_edid(struct drm_connector *connector,
>  			  struct i2c_adapter *adapter);
>  struct edid_base_block *drm_edid_get_base_block(struct i2c_adapter *adapter);
>  u32 drm_edid_get_panel_id(struct edid_base_block *base_block);
> +bool drm_edid_has_monitor_string(struct edid_base_block *base_block, const char *str);
>  struct edid *drm_get_edid_switcheroo(struct drm_connector *connector,
>  				     struct i2c_adapter *adapter);
>  struct edid *drm_edid_duplicate(const struct edid *edid);

-- 
Jani Nikula, Intel