linux-kernel - Re: [PATCH v2 00/13] serial: 8250

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Message-ID: <20240906143851.21c97ef9@SWDEV2.connecttech.local>
Date: Fri, 6 Sep 2024 14:38:51 -0400
From: Parker Newman <parker@...est.io>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Parker Newman <pnewman@...necttech.com>, linux-kernel@...r.kernel.org,
 linux-serial@...r.kernel.org, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>
Subject: Re: [PATCH v2 00/13] serial: 8250_exar: Clean up the driver

On Fri, 6 Sep 2024 17:42:26 +0300
Andy Shevchenko <andriy.shevchenko@...ux.intel.com> 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@...ux.intel.com> 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@...ux.intel.com> 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?

Thanks,
Parker