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

[Parker Newman <parker@finest.io>]

On Fri, 20 Sep 2024 17:45:15 +0300
Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:

> 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.
> 

Sounds good, I will change in v3.

> > 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.)
> 

Thanks! This is very helpful.