Hi,
On Mon, Sep 6, 2021 at 3:05 AM Jani Nikula jani.nikula@linux.intel.com wrote:
+{
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.
I'm not 100% sure, but I think you're suggesting having this function return a `struct edid_panel_id` or something like that. Is that right? Maybe that would look something like this?
struct edid_panel_id { char vendor[4]; u16 product_id; }
...or perhaps this (untested, but I think it works):
struct edid_panel_id { u16 vend_c1:5; u16 vend_c2:5; u16 vend_c3:5; u16 product_id; }
...and then change `struct edid_quirk` to something like this:
static const struct edid_quirk { struct edid_panel_id panel_id; u32 quirks; } ...
Is that correct? There are a few downsides that I can see:
a) I think the biggest downside is the inability compare with "==". I don't believe it's legal to compare structs with "==" in C. Yeah, we can use memcmp() but that feels more awkward to me.
b) Unless you use the bitfield approach, it takes up more space. I know it's not a huge deal, but the format in the EDID is pretty much _forced_ to fit in 32-bits. The bitfield approach seems like it'd be more awkward than my encoding macros.
-Doug