On Sun, Jan 12, 2025 at 10:58 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > Hi Krzysztof, > > On Sat, Jan 11, 2025 at 12:00 PM Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote: > > On 10/01/2025 15:14, Bartosz Golaszewski wrote: > > >> At24 EEPROMs differ from '595 shift registers in that they provide an > > >> API with multiple commands, and some commands or parameter bits may > > >> differ among different implementations (but usually these differences > > >> are called quirks). > > >> > > >> All '595 (I'm deliberately writing it like that) shift registers > > >> should be 100% compatible, modulo some electrical specifications > > >> (voltage levels, maximum speed, power consumption, ...). > > >> > > >> Interestingly, the driver is called gpio-74x164.c, while no '164 > > >> compatible value is present. Most important difference is that the > > >> '164 lacks the output latch, which is used as chip-select with SPI[1]. > > >> > > >>>> I'm especially against introducing a new, vendor-specific (On Semi, in > > >>>> this case) name; if we really want to introduce a new compatible, at > > >>>> least make it as generic as possible, i.e. `generic,74x595`, or even > > >>>> `generic,spi-shift-register-output`. > > >>> > > >>> If anything, that would have to be the fallback that the driver knows. > > >>> The first string in the compatible property has to have an actual > > >>> vendor (I think, I'll let DT maintainers correct me). > > >> > > >> For the inverse operation (parallel in, serial out), there's just > > >> "pisosr-gpio". > > > > > > Ok, I admit I don't know the correct next step. I'll wait for > > > Krzysztof, Rob or Conor to chime in (on the subject of representing > > > reality - the actual manufacturer - in DTS) and then possibly just > > > remove patches 1-2 from my tree. > > > > Well, folks, I don't know the exact device, so maybe there is no point > > in a new compatible if there is a claim all devices have same interface > > and documenting all of them would result in 1000 redundant > > compatibles... but OTOH, that's what we still do with jedec,spi and > > at24, so if we can add specific compatibles for these, we can do same > > also here. > > Except that we don't for jedec,spi, unfortunately[1]. > > At24 and jedec,spi use a complex programming API, with lots of room > for deviation and extension. '595 is a pure hardware part[2]: it is > just a shift register (driven by SPI clock and MOSI) with a latch > (driven by deasserting SPI chip select), without room for deviation. > Anything that behaves differently is not a jelly-bean '595 part. > > [1] "[PATCH] dt-bindings: mtd: jedec,spi-nor: Document support for > more MT25QU parts' > https://lore.kernel.org/all/363186079b4269891073f620e3e2353cf7d2559a.1669988238.git.geert+renesas@xxxxxxxxx > > [2] Ignoring the rumor that all Microchip I/O expanders are actually > pre-programmed PIC microcontrollers ;-) It's late into the cycle and as it's not clear whether we really need the new compatible or not, I removed the two patches from my queue. Let's revisit it in the next release. Bartosz
