Hi Andy, 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. Regards, Hans
