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From: Sam Edwards <sam@turingpi.com>
Date: Tue, 19 Mar 2024 22:19:53 -0600
Message-ID: <CAF8uH3tYaUwhkkeFuY+PdsnSPqeTtWtOsB_hy9oOjF=f-2Hdaw@mail.gmail.com>
Subject: [RESEND RFC PATCH 0/5] Enhancements for mv64xxx I2C driver
To: Gregory CLEMENT <gregory.clement@bootlin.com>, Andi Shyti <andi.shyti@kernel.org>
Cc: linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org
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Salutations, Linux I2C team!

Sorry about the resend; it seems my mail client "helpfully" swallowed the
newlines on any line consisting only of whitespace, garbling the patches.

I am working with an Allwinner T113-s3 based board; the internal I2C bus of
which has a Realtek RTL8370MB-CG Ethernet switch coexisting with other I2C
devices. The RTL8370MB-CG deviates from "conventional" I2C read operations
in that it expects the hardware register after the addr+read byte before it
turns around the bus to send the value. For this reason, the `realtek-smi`
driver currently implements the protocol via bit-banging. However, I am in the
process of developing a separate patch series to promote this driver to a
"full" I2C driver, leveraging I2C_M_NOSTART to support this odd read operation.

In anticipation of that, I am preparing this series comprising five patches to
improve the functionality and reliability of the I2C adapter enough to support
this kind of device. I have heavily tested these changes on the Allwinner-style
mv64xxx core, but not the Marvell-style, and have not been able to test 10-bit
addressing. I would greatly appreciate if anyone here could test this series,
especially on non-Allwinner boards and/or boards with 10-bit devices.

I'm a bit skeptical of using I2C_M_NOSTART for this purpose. The driver does
not (and cannot) support "just any" use of I2C_M_NOSTART, so it may be
inappropriate to claim the I2C_FUNC_NOSTART capability. On the other hand, I
searched high and low and couldn't find any use of I2C_M_NOSTART that
*wouldn't* be supported by this change, so this could very well be exactly what
clients understand I2C_FUNC_NOSTART to mean. Given that the alternative would
be inventing a new flag ("I2C_M_READEXTRA"?) and figuring out how to supply
input bytes and output bytes in the same i2c_msg, I opted for the NOSTART
route instead.

I look forward to any feedback, bug reports, test results, questions, concerns,
commentary, or discussion that you can offer!

Best regards,
Sam

Sam Edwards (5):
  i2c: mv64xxx: Clear bus errors before transfer
  i2c: mv64xxx: Clean up the private data struct
  i2c: mv64xxx: Refactor FSM
  i2c: mv64xxx: Allow continuing after read
  i2c: mv64xxx: Implement I2C_FUNC_NOSTART

 drivers/i2c/busses/i2c-mv64xxx.c | 430 ++++++++++++++++++++++---------
 1 file changed, 302 insertions(+), 128 deletions(-)

--
2.43.2