On Wed, 01 Sep 2021, Douglas Anderson <dianders@xxxxxxxxxxxx> wrote: > EDIDs have 32-bits worth of data which is intended to be used to > uniquely identify the make/model of a panel. This has historically > been used only internally in the EDID processing code to identify > quirks with panels. > > We'd like to use this panel ID in panel-simple to identify which panel > is hooked up and from that information figure out power sequence > timings. Let's expose this information from the EDID code and also > allow it to be accessed early, before a connector has been created. > > To make matching in the panel-simple code easier, we'll return the > panel ID as a 32-bit value. We'll provide some functions for > converting this value back and forth to something more human readable. > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > --- > > Changes in v3: > - Decode hex product ID w/ same endianness as everyone else. > > drivers/gpu/drm/drm_edid.c | 59 ++++++++++++++++++++++++++++++++++++++ > include/drm/drm_edid.h | 47 ++++++++++++++++++++++++++++++ > 2 files changed, 106 insertions(+) > > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c > index a22c38482a90..ac128bc3478a 100644 > --- a/drivers/gpu/drm/drm_edid.c > +++ b/drivers/gpu/drm/drm_edid.c > @@ -2086,6 +2086,65 @@ struct edid *drm_get_edid(struct drm_connector *connector, > } > EXPORT_SYMBOL(drm_get_edid); > > +/** > + * drm_get_panel_id - Get a panel's ID through DDC > + * @adapter: I2C adapter to use for DDC > + * > + * This function reads the first block of the EDID of a panel and (assuming > + * that the EDID is valid) extracts the ID out of it. The ID is a 32-bit value > + * (16 bits of manufacturer ID and 16 bits of per-manufacturer ID) that's > + * supposed to be different for each different modem of panel. > + * > + * This function is intended to be used during early probing on devices where > + * more than one panel might be present. Because of its intended use it must > + * assume that the EDID of the panel is correct, at least as far as the ID > + * is concerned (in other words, we don't process any overrides here). > + * > + * NOTE: it's expected that this function and drm_do_get_edid() will both > + * be read the EDID, but there is no caching between them. Since we're only > + * reading the first block, hopefully this extra overhead won't be too big. > + * > + * Return: A 32-bit ID that should be different for each make/model of panel. > + * See the functions encode_edid_id() and decode_edid_id() for some > + * details on the structure of this ID. > + */ > +u32 drm_get_panel_id(struct i2c_adapter *adapter) Please call it drm_edid_get_panel_id() because that's what it is, and this is in drm_edid.[ch]. > +{ > + struct edid *edid; > + u32 val; > + > + edid = drm_do_get_edid_blk0(drm_do_probe_ddc_edid, adapter, NULL, NULL); > + > + /* > + * There are no manufacturer IDs of 0, so if there is a problem reading > + * the EDID then we'll just return 0. > + */ > + if (IS_ERR_OR_NULL(edid)) > + return 0; > + > + /* > + * In theory we could try to de-obfuscate this like edid_get_quirks() > + * does, but it's easier to just deal with a 32-bit number. Hmm, but is it, really? AFAICT this is just an internal representation for a table, where it could just as well be stored in a struct that could be just as compact now, but extensible later. You populate the table via an encoding macro, then decode the id using a function - while it could be in a format that's directly usable without the decode. If suitably chosen, the struct could perhaps be reused between the quirks code and your code. > + * > + * NOTE that we deal with endianness differently for the top half > + * of this ID than for the bottom half. The bottom half (the product > + * id) gets decoded as little endian by the EDID_PRODUCT_ID because > + * that's how everyone seems to interpret it. The top half (the mfg_id) > + * gets stored as big endian because that makes encode_edid_id() and > + * decode_edid_id() easier to write (it's easier to extract the ASCII). > + * It doesn't really matter, though, as long as the number here is > + * unique. > + */ > + val = (u32)edid->mfg_id[0] << 24 | > + (u32)edid->mfg_id[1] << 16 | > + (u32)EDID_PRODUCT_ID(edid); > + > + kfree(edid); > + > + return val; > +} > +EXPORT_SYMBOL(drm_get_panel_id); > + > /** > * drm_get_edid_switcheroo - get EDID data for a vga_switcheroo output > * @connector: connector we're probing > diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h > index deccfd39e6db..73da40d0b5d1 100644 > --- a/include/drm/drm_edid.h > +++ b/include/drm/drm_edid.h > @@ -508,6 +508,52 @@ static inline u8 drm_eld_get_conn_type(const uint8_t *eld) > return eld[DRM_ELD_SAD_COUNT_CONN_TYPE] & DRM_ELD_CONN_TYPE_MASK; > } > > +/** > + * encode_edid_id - Encode an ID for matching against drm_get_panel_id() > + * @vend_chr_0: First character of the vendor string. > + * @vend_chr_2: Second character of the vendor string. > + * @vend_chr_3: Third character of the vendor string. > + * @product_id: The 16-bit product ID. > + * > + * This is a macro so that it can be calculated at compile time and used > + * as an initializer. > + * > + * For instance: > + * encode_edid_id('B', 'O', 'E', 0x2d08) => 0x09e52d08 > + * > + * Return: a 32-bit ID per panel. > + */ > +#define encode_edid_id(vend_chr_0, vend_chr_1, vend_chr_2, product_id) \ > + ((((u32)(vend_chr_0) - '@') & 0x1f) << 26 | \ > + (((u32)(vend_chr_1) - '@') & 0x1f) << 21 | \ > + (((u32)(vend_chr_2) - '@') & 0x1f) << 16 | \ > + ((product_id) & 0xffff)) > + > +/** > + * decode_edid_id - Decode a panel ID from encode_edid_id() > + * @panel_id: The panel ID to decode. > + * @vend: A 4-byte buffer to store the 3-letter vendor string plus a '\0' > + * termination > + * @product_id: The product ID will be returned here. > + * > + * For instance, after: > + * decode_edid_id(0x09e52d08, vend, &product_id) > + * These will be true: > + * vend[0] = 'B' > + * vend[1] = 'O' > + * vend[2] = 'E' > + * vend[3] = '\0' > + * product_id = 0x2d08 > + */ > +static inline void decode_edid_id(u32 panel_id, char vend[4], u16 *product_id) > +{ > + *product_id = (u16)(panel_id & 0xffff); > + vend[0] = '@' + ((panel_id >> 26) & 0x1f); > + vend[1] = '@' + ((panel_id >> 21) & 0x1f); > + vend[2] = '@' + ((panel_id >> 16) & 0x1f); > + vend[3] = '\0'; > +} I think the names here could use a drm_edid_ prefix too. Maybe drm_edid_encode_panel_id and drm_edid_decode_panel_id, aligning nicely with drm_edid_get_panel_id. BR, Jani. > + > bool drm_probe_ddc(struct i2c_adapter *adapter); > struct edid *drm_do_get_edid(struct drm_connector *connector, > int (*get_edid_block)(void *data, u8 *buf, unsigned int block, > @@ -515,6 +561,7 @@ struct edid *drm_do_get_edid(struct drm_connector *connector, > void *data); > struct edid *drm_get_edid(struct drm_connector *connector, > struct i2c_adapter *adapter); > +u32 drm_get_panel_id(struct i2c_adapter *adapter); > 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 Open Source Graphics Center