Re: [PATCH v2 1/4] misc: eeprom: eeprom_93cx6: Add quirk for extra read clock cycle

Andy Shevchenko
2024-09-20T14:45:20Z

On Fri, Sep 20, 2024 at 10:03:21AM -0400, Parker Newman wrote:
> From: Parker Newman <pnewman@connecttech.com>
>
> This patch adds a quirk similar to eeprom_93xx46 to add an extra clock
> cycle before reading data from the EEPROM.
>
> The 93Cx6 family of EEPROMs output a "dummy 0 bit" between the writing
> of the op-code/address from the host to the EEPROM and the reading of
> the actual data from the EEPROM.
>
> More info can be found on page 6 of the AT93C46 datasheet (linked below).
> Similar notes are found in other 93xx6 datasheets.
>
> In summary the read operation for a 93Cx6 EEPROM is:
> Write to EEPROM: 110[A5-A0] (9 bits)
> Read from EEPROM: 0[D15-D0] (17 bits)
>
> Where:
> 110 is the start bit and READ OpCode
> [A5-A0] is the address to read from
> 0 is a "dummy bit" preceding the actual data
> [D15-D0] is the actual data.
>
> Looking at the READ timing diagrams in the 93Cx6 datasheets the dummy
> bit should be clocked out on the last address bit clock cycle meaning it
> should be discarded naturally.
>
> However, depending on the hardware configuration sometimes this dummy
> bit is not discarded. This is the case with Exar PCI UARTs which require
> an extra clock cycle between sending the address and reading the data.
>
> Link: https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-5193-SEEPROM-AT93C46D-Datasheet.pdf

JFYI: You may also convert this to Datasheet: tag (we have a history of it
mostly in IIO subsystem), basically replacing word Link by Datasheet in the
above line.

> Signed-off-by: Parker Newman <pnewman@connecttech.com>

Code wise LGTM now,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

(Do not forget to embed this tag into a new version. With this the `b4` tool
is quite helpful, so the workflow is to checkout a new branch in your local
Git tree, like `git checkout -b exar-93xx46 v6.12-rc1` then taking a message
ID from email of this thread — any should succeed, but cover letter's one
for sure — run the following `b4 am $<message ID>`. It will print the hints
what to do next, something like `git am $<patch_title>.mbx`. Then you can
continue with `git rebase --interactive v6.12-rc1` if the code or other
stuff in the commit message needs to be updated.)

--
With Best Regards,
Andy Shevchenko