Hi Geert, thank you for the review! > Note that R-Car Gen4 (incl. R-Car S4) has ICFBSCR bits related to > Slave Clock Stretch Select (which is not yet supported by the driver). Thanks for the heads up. I'd need more information about the use case of these bits. Seperate task. > According to the Programming Examples in the docs for R-Car Gen3, > R-Car V3U, S4-8, and V4H, I2C must be reset "at the beginning of > transmission and reception procedure", so not only for DMA. Sadly, this is vague. If you look at the example for a combined write-then-read transfer, then you see that only one reset is done, i.e.: reset -> write -> rep_start -> read That would mean that we don't need a reset per read/write message of a transfer. But a reset per transfer then? I would wonder why because we could also have a super long transfer with lots of read/write messages in it. Do we need a reset then inbetween? Or is it really dependant on the STOP bit being transferred? I guess these are all questions for the HW team, though. I was reluctant to add the reset too often because my measurements back then showed that it costs around 5us every time. Annoying. Maybe I should take it easy and follow the documentation. But then I am still not sure if a large transfer with way more than two messages are OK without reset? I will ask the HW team. > Also, you didn't the touch the checks in rcar_i2c_cleanup_dma(): ... > and rcar_i2c_master_xfer(): ... > > Don't these apply to R-Car Gen4? I can't easily find where this quirk > is documented (perhaps just as a commit in the BSP?), but at least the > "Usage note for DMA mode of Receive Operation" looks identical for > R-Car Gen3 and for the various R-Car Gen4 variants. My memory played a trick on me here. I asked Shimoda-san about this issue on Gen4. I thought I got an answer that it was fixed, so I left the code Gen3 only. But he actually never got a reply and I forgot to ping about it. The latest documentation has now a "usage note for DMA mode" about it implying that the issue is still present on Gen4 :( > BTW, depending on the answers to my questions above, you may want to > replace the rcar_i2c_type enum by a feature mask... That might be an option. I need to reshuffle my I2C patches first, though. I'll send some cleanups first to have them out of the way. Then, I will respin Gen4 support and take care of the DMA RX issue and the new reset handling there. Thank you for your input! All the best, Wolfram
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