Re: [PATCH v2] i2c: qcom-cci: always enable SCL clock stretching

[Andi Shyti <andi.shyti@kernel.org>]

Hi Hitesh,

Please don't send next versions as --in-reply-to, it makes life
difficult.

On Mon, Sep 21, 2026 at 06:49:54PM +0530, Hitesh Patel wrote:
> Every CCI timing table except the msm8953 fast-plus one leaves SCL
> clock stretching disabled in MISC_CTL. A slave that holds SCL low is
> then not waited for: the master keeps its own clock timing and the
> transfer fails with a NACK or returns corrupt data.
> 
> This is hit with a camera reached through a GMSL serializer/
> deserializer I2C tunnel (MAX9296A/MAX96717 on the RB3 Gen2 vision
> mezzanine, SC7280 CCI v2 at 100 kHz). The deserializer acknowledges
> the address locally, forwards the transaction over the coax link and
> stretches SCL until the remote side has completed it, which takes well
> over one clock period. Without stretching the register reads of the
> sensor behind the link intermittently return garbage and writes are
> dropped, which shows up as random sensor init failures.
> 
> Clock stretching is part of the I2C specification for every speed
> mode and a device that does not stretch is unaffected by it, so there
> is no reason to make it a per-table parameter. Set the bit
> unconditionally and drop the scl_stretch_en field.
> 
> Signed-off-by: Hitesh Patel <hitesh@ebytelogic.com>

I'll wait for an ack from Konrad here.

Thanks,
Andi