On 29/07/2022 16:47, Andy Shevchenko wrote: > 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?)? Only V4L2: an EDID describes the capabilities of a video sink (e.g. a display), so it is specific to video receivers, and that's the domain of V4L2. Regards, Hans
