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From: Hsin-Yi Wang <hsinyi@chromium.org>
Date: Mon, 4 Mar 2024 18:11:52 -0800
Message-ID: <CAJMQK-i284bO=dSOZTsgJaMMWDCqXmYB_SDJbhx3U1s-U==S2A@mail.gmail.com>
Subject: Re: [PATCH v3 2/4] drm/edid: Add a function to check monitor string
To: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Douglas Anderson <dianders@chromium.org>, Neil Armstrong <neil.armstrong@linaro.org>, 
	Jessica Zhang <quic_jesszhan@quicinc.com>, Sam Ravnborg <sam@ravnborg.org>, 
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>, Maxime Ripard <mripard@kernel.org>, 
	Thomas Zimmermann <tzimmermann@suse.de>, David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>, 
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, 
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
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On Mon, Mar 4, 2024 at 4:09=E2=80=AFPM Jani Nikula <jani.nikula@linux.intel=
com> wrote:
>
> On Mon, 04 Mar 2024, Hsin-Yi Wang <hsinyi@chromium.org> wrote:
> > On Mon, Mar 4, 2024 at 12:38=E2=80=AFPM Jani Nikula <jani.nikula@linux.=
intel.com> wrote:
> >>
> >> 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 stri=
ng.
> >> >
> >> > One of the use cases is fetching panel from a list of panel names, s=
ince
> >> > some panel vendors put the monitor name after EDID_DETAIL_MONITOR_ST=
RING
> >> > 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_bl=
ock *base_block)
> >> >  }
> >> >  EXPORT_SYMBOL(drm_edid_get_panel_id);
> >> >
> >> > +/**
> >> > + * drm_edid_has_monitor_string - Check if a EDID base block has cer=
tain string.
> >> > + * @base_block: EDID base block to check.
> >> > + * @str: pointer to a character array to hold the string to be chec=
ked.
> >> > + *
> >> > + * Check if the detailed timings section of a EDID base block has t=
he given
> >> > + * string.
> >> > + *
> >> > + * Return: True if the EDID base block contains the string, false o=
therwise.
> >> > + */
> >> > +bool drm_edid_has_monitor_string(struct edid_base_block *base_block=
, const char *str)
> >> > +{
> >> > +     unsigned int i, j, k, buflen =3D strlen(str);
> >> > +
> >> > +     for (i =3D 0; i < EDID_DETAILED_TIMINGS; i++) {
> >> > +             struct detailed_timing *timing =3D &base_block->edid.d=
etailed_timings[i];
> >> > +             unsigned int size =3D ARRAY_SIZE(timing->data.other_da=
ta.data.str.str);
> >> > +
> >> > +             if (buflen > size || timing->pixel_clock !=3D 0 ||
> >> > +                 timing->data.other_data.pad1 !=3D 0 ||
> >> > +                 (timing->data.other_data.type !=3D EDID_DETAIL_MON=
ITOR_NAME &&
> >> > +                  timing->data.other_data.type !=3D EDID_DETAIL_MON=
ITOR_STRING))
> >> > +                     continue;
> >> > +
> >> > +             for (j =3D 0; j < buflen; j++) {
> >> > +                     char c =3D timing->data.other_data.data.str.st=
r[j];
> >> > +
> >> > +                     if (c !=3D str[j] ||  c =3D=3D '\n')
> >> > +                             break;
> >> > +             }
> >> > +
> >> > +             if (j =3D=3D buflen) {
> >> > +                     /* Allow trailing white spaces. */
> >> > +                     for (k =3D j; k < size; k++) {
> >> > +                             char c =3D timing->data.other_data.dat=
a.str.str[k];
> >> > +
> >> > +                             if (c =3D=3D '\n')
> >> > +                                     return true;
> >> > +                             else if (c !=3D ' ')
> >> > +                                     break;
> >> > +                     }
> >> > +                     if (k =3D=3D size)
> >> > +                             return true;
> >> > +             }
> >> > +     }
> >> > +
> >> > +     return false;
> >> > +}
> >> > +
> >>
> >> So we've put a lot of effort into converting from struct edid to struc=
t
> >> 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 cons=
t
> >>   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=
.
> >
> > To clarify:
> > struct drm_edid currently is only internal to drm_edid.c. So with
> > change we will have to move it to the header drm_edid.h
>
> Absolutely not, struct drm_edid must remain an opaque type. The point is
> that you ask drm_edid.c if there's a match or not, and the panel code
> does not need to care what's inside struct drm_edid.
>

Sorry I might be misunderstanding about the requests here:

If drm_edid should remain opaque, then struct drm_edid remains opaque,
drm_edid_match() should take struct edid *edid as a parameter? just as
other exposed functions in drm_edid.

If panel edp doesn't hold drm_edid returned from
drm_edid_read_base_block(), what should it use to iterate the
edp_panels array?

for (panel =3D edp_panels; panel->panel_id; panel++)
    if(drm_edid_match(drm_edid, panel->ident))
        ...

> >
> >>
> >> - Remove function:
> >>
> >>     u32 drm_edid_get_panel_id(struct i2c_adapter *adapter);
> >>
> >
> > Probably change to u32 drm_edid_get_panel_id(const struct drm_edid
> > *);? Given that we still need to parse id from
> > drm_edid_read_base_block().
>
> No, we no longer need to parse the id outside of drm_edid.c. You'll have
> the id's in panel code in the form of struct drm_edid_ident (or
> whatever), and use the match function to see if the opaque drm_edid
> matches.
>
> >
> >> - Refactor edid_quirk_list to use the same id struct and match functio=
n
> >>   and mechanism within drm_edid.c (can be follow-up too).
> >>
> >
> > edid_quirk currently doesn't have panel names in it, and it might be a
> > bit difficult to get all the correct names of these panels without
> > having the datasheets.
> > One way is to leave the name as null and if the name is empty and skip
> > matching the name in drm_edid_match().
>
> Exactly. NULL in drm_edid_ident would mean "don't care". I think most of
> the ones in panel code also won't use the name for matching.
>
> BR,
> Jani.
>
> >
> >> - 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, becau=
se
> >>   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 *connecto=
r,
> >> >                                    struct i2c_adapter *adapter);
> >> >  struct edid *drm_edid_duplicate(const struct edid *edid);
> >>
> >> --
> >> Jani Nikula, Intel
>
> --
> Jani Nikula, Intel