On Mon, 9 Sep 2024 13:06:26 +0300 Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote: > On Fri, Sep 06, 2024 at 02:38:51PM -0400, Parker Newman wrote: > > On Fri, 6 Sep 2024 17:42:26 +0300 > > Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote: > > > On Fri, Sep 06, 2024 at 10:33:54AM -0400, Parker Newman wrote: > > > > On Fri, 6 Sep 2024 17:24:44 +0300 > > > > Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote: > > > > > On Fri, Sep 06, 2024 at 09:51:41AM -0400, Parker Newman wrote: > > > > > > On Fri, 6 Sep 2024 15:46:51 +0300 > > > > > > Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote: > > > > > > > On Fri, May 03, 2024 at 02:33:03PM -0400, Parker Newman wrote: > > ... > > > > > > > > Sorry for blast from the past, but I have some instersting information > > > > > > > for you. We now have spi-gpio and 93c46 eeprom drivers available to be > > > > > > > used from others via software nodes, can you consider updating your code > > > > > > > to replace custom bitbanging along with r/w ops by the instantiating the > > > > > > > respective drivers? > > > > > > > > > > > > Hi Andy, > > > > > > The Exar UARTs don't actually use MPIO/GPIO for the EEPROM. > > > > > > They have a dedicated "EEPROM interface" which is accessed by the > > > > > > REGB (0x8E) register. It is a very simple bit-bang interface though, > > > > > > one bit per signal. > > > > > > > > > > > > I guess in theory I could either add GPIO wrapper to toggle these bits > > > > > > and use the spi-gpio driver but I am not sure if that really improves things? > > > > > > Maybe using the spi-bitbang driver directly is more appropriate? > > > > > > What do you think? > > > > > > > > > > Yes, spi-bitbang seems better in this case. > > > > > > > > I will try to make some time to implement this... Or if someone else from the > > > > community wants to take this on in the mean time I am certainly happy to test > > > > and help out! > > > > > > Sure, I shared this thought due to having lack of time to look myself, > > > but I prepared the above mentioned drivers to make them work in this case. > > > (If you are curios, see the Git history for the last few releases with > > > --author="Andy Shevchenko") > > > > > > > Looking into it a bit more I think we could just use the eeprom_93cx6 > > driver without any SPI layer. Just need to add simple register_read() > > and register_write() functions to read/write the REB register. > > > > That should be a pretty easy change to make, I can try to make that > > change soon unless anyone has any objections to that method? > > Thank you, this is pretty wonderful news! > I have this mostly working however there is one issue. The eeprom_93cx6 driver doesn't seem to discard the "dummy bit" the 93C46 EEPROM outputs between the writing of the op-code/address to the EEPROM and the reading of the data from the EEPROM. More info can be found on page 6 of the AT93C46 datasheet. I see similar notes in other 93C46/93C56/93C66 datasheets. Link: https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-5193-SEEPROM-AT93C46D-Datasheet.pdf In summary the read operation for the AT93C46 EEPROM is: Write to EEPROM : 110[A5-A0] (9 bits) Read from EEPROM: 0[D15-D0] (17 bits) Where 110 is the READ OpCode, [A5-A0] is the address to read from, 0 is a "dummy bit" and then [D15-D0] is the actual data. I am seeing the "correct" values being read from the EEPROM when using the eeprom_93cx6 driver but they are all shifted right by one because the dummy 0 bit is not being discarded. The confusing part is the eeprom_93cx6 driver has behaved the same since at least 2009 and half a dozen or so other drivers use it. I am not sure if they just work around and/or live with this bug or if they have different HW that handles the extra dummy bit? I am hesitant to "fix" the eeprom_93cx6 driver and potentially break the other users of it. I could add a flag to the eeprom_93cx6 struct to work around this issue... Unless anyone else has some ideas or input? Thanks, Parker
