On Fri, Jul 29, 2022 at 2:11 PM Hans Verkuil <hverkuil-cisco@xxxxxxxxx> wrote: > On 29/07/2022 14:00, Andy Shevchenko wrote: > > On Fri, Jul 29, 2022 at 9:21 AM Hans Verkuil <hverkuil-cisco@xxxxxxxxx> wrote: > >> On 28/07/2022 22:56, Andy Shevchenko wrote: > >>> On Thu, Jul 28, 2022 at 3:23 PM Hans Verkuil <hverkuil-cisco@xxxxxxxxx> wrote: > >>>> On 28/07/2022 14:02, Andy Shevchenko wrote: > >>>>> On Thursday, July 28, 2022, Erling Ljunggren <hljunggr@xxxxxxxxx <mailto:hljunggr@xxxxxxxxx>> wrote: > >>> > >>>>> Support reading and writing the EDID EEPROM through the > >>>>> v4l2 API. > >>>>> > >>>>> Why the normal way of representing as a memory (we have framework and drivers) can’t work? > >>>> > >>>> Because support for EDID for video sinks is already part of the media subsystem (V4L2). > >>>> Normally it is integrated into an HDMI receiver, but in this case it is just the EDID > >>>> support without the video receiver. It belongs in drivers/media in any case since EDIDs > >>>> are closely tied to media. > >>> > >>> It's fine. From the Linux perspective we do not reduplicate the > >>> drivers that are done by other frameworks, right? > >>> > >>>>> Moreover, this driver seems limited in support of variety of the eeprom chips. > >>>> > >>>> Not quite sure what you mean. The cat24c208 is what this was developed for and > >>>> the only one we have. > >>>> > >>>> Note that an EDID EEPROM != a regular EEPROM: it has to support the VESA E-DDC > >>>> standard, which a normal EEPROM doesn't. So these devices are specifically made > >>>> for this use-case. > >>> > >>> What is the difference from a programming interface? > >>> Can the nvmem driver(s) be reused (at24?)? > >> > >> No. EDID EEPROM devices are specific to storing EDIDs: they have two i2c > >> ports, one connected to (typically) the HDMI bus (DDC lines) allowing a > >> video source to read the EDID, the other is connected to the SoC to write to > >> and configure the device. The HDMI bus side has two i2c addresses (reading the > >> EEPROM and to write to the segment address for EDIDs > 256 bytes), the SoC > >> side has three i2c addresses: to configure the behavior, the segment address, > >> and to write the EDID from the SoC. > >> > >> So it is a much more complex device than a regular eeprom, and it really > >> is dedicated to EDIDs only. > > > > Thanks for the explanation, but it's still unclear what the > > differences are in the programming interface there. Perhaps you may > > simply register a platform device in this driver and reuse the rest > > from at24? > > No, it's really different from a regular eeprom. > > >> Also note that the V4L2 API is already used to get/set EDIDs, everything is > >> in place for supporting that, including support for parsing EDIDs for the > >> physical address, which is something that is needed if this is combined with > >> HDMI CEC hardware. It's not implemented in this driver since it is not > >> needed in our use-case, but that might change in the future. > >> > >> And by using the V4L2 API you can use v4l2-ctl --get-edid and --set-edid > >> out of the box, using the standard API for EDIDs. > > > > Bonus question: we have cat24c04/cat24c05 are recognized by at24 > > already, are they different to cat24c08? > > > > Yes, they are different. Thanks for your patience and elaboration, I got it. Would this driver be used only by v4l2? Or potentially some other hardware may need it (DRM?)? -- With Best Regards, Andy Shevchenko
