Re: [PATCH AUTOSEL 5.12 42/43] powerpc/fsl: set fsl,i2c-erratum-a004447 flag for P2041 i2c controllers

[Sasha Levin]

On Fri, Jun 04, 2021 at 12:58:54AM +0000, Chris Packham wrote:
> On 4/06/21 12:42 pm, Michael Ellerman wrote:
> > Sasha Levin <sashal@xxxxxxxxxx> writes:
> > > From: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
> > >
> > > [ Upstream commit 7adc7b225cddcfd0f346d10144fd7a3d3d9f9ea7 ]
> > >
> > > The i2c controllers on the P2040/P2041 have an erratum where the
> > > documented scheme for i2c bus recovery will not work (A-004447). A
> > > different mechanism is needed which is documented in the P2040 Chip
> > > Errata Rev Q (latest available at the time of writing).
> > >
> > > Signed-off-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
> > > Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > > Signed-off-by: Wolfram Sang <wsa@xxxxxxxxxx>
> > > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > > ---
> > >   arch/powerpc/boot/dts/fsl/p2041si-post.dtsi | 16 ++++++++++++++++
> > >   1 file changed, 16 insertions(+)
> > This patch (and the subsequent one), just set a flag in the device tree.
> >
> > They have no effect unless you also backport the code change that looks
> > for that flag, which was upstream commit:
> >
> >    8f0cdec8b5fd ("i2c: mpc: implement erratum A-004447 workaround")
>
> That change itself isn't cherry-pick able without
>
> 65171b2df15e ("i2c: mpc: Make use of i2c_recover_bus()")
>
> and in between 65171b2df15e and 8f0cdec8b5fd are a bunch of cleanups and
> a fairly major rewrite which may also affect the cherry-pick ability.
>
> > AFAICS you haven't picked that one up for any of the stable trees.
> >
> > I'll defer to Chris & Wolfram on whether it's a good idea to take the
> > code change for stable.
>
> We have been doing some extra QA on our end for the "i2c: mpc: Refactor
> to improve responsiveness" and "P2040/P2041 i2c recovery erratum" series
> which hasn't thrown up any issues. But it's still a lot of new code and
> at some point we're going to run into API changes.
>
> Given the fact that it's starting to snowball one might err on the side
> of caution.
>
> > I guess it's harmless to pick these two patches, but it's also
> > pointless. So I think you either want to take all three, or drop these
> > two.
>
> At a minimum you need
>
> 65171b2df15e ("i2c: mpc: Make use of i2c_recover_bus()")
> 8f0cdec8b5fd ("i2c: mpc: implement erratum A-004447 workaround")
> 7adc7b225cdd ("powerpc/fsl: set fsl,i2c-erratum-a004447 flag for P2041
> i2c controllers")
> 19ae697a1e4e ("powerpc/fsl: set fsl,i2c-erratum-a004447 flag for P1010
> i2c controllers")

I'll take the two additional commits, thanks!

--
Thanks,
Sasha