linux-kernel - Re: [PATCH v6 00/15] arm64: Self-hosted trace related errata workarounds

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Date:   Fri, 22 Oct 2021 09:13:11 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Will Deacon <will@...nel.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        catalin.marinas@....com, anshuman.khandual@....com,
        mike.leach@...aro.org, leo.yan@...aro.org, maz@...nel.org,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 00/15] arm64: Self-hosted trace related errata
 workarounds

On Fri, Oct 22, 2021 at 09:14:38AM +0200, Greg KH wrote:
> On Thu, Oct 21, 2021 at 05:47:31PM +0100, Will Deacon wrote:
> > Hi Mathieu,
> > 
> > [CC Greg]
> > 
> > On Thu, Oct 21, 2021 at 10:35:31AM -0600, Mathieu Poirier wrote:
> > > On Thu, Oct 21, 2021 at 09:53:14AM +0100, Will Deacon wrote:
> > > > On Wed, Oct 20, 2021 at 09:42:07AM -0600, Mathieu Poirier wrote:
> > > > > On Tue, Oct 19, 2021 at 05:31:38PM +0100, Suzuki K Poulose wrote:
> > > > > > Suzuki K Poulose (15):
> > > > > >   arm64: Add Neoverse-N2, Cortex-A710 CPU part definition
> > > > > >   arm64: errata: Add detection for TRBE overwrite in FILL mode
> > > > > >   arm64: errata: Add workaround for TSB flush failures
> > > > > >   arm64: errata: Add detection for TRBE write to out-of-range
> > > > > >   coresight: trbe: Add a helper to calculate the trace generated
> > > > > >   coresight: trbe: Add a helper to pad a given buffer area
> > > > > >   coresight: trbe: Decouple buffer base from the hardware base
> > > > > >   coresight: trbe: Allow driver to choose a different alignment
> > > > > >   coresight: trbe: Add infrastructure for Errata handling
> > > > > >   coresight: trbe: Workaround TRBE errata overwrite in FILL mode
> > > > > >   coresight: trbe: Add a helper to determine the minimum buffer size
> > > > > >   coresight: trbe: Make sure we have enough space
> > > > > >   coresight: trbe: Work around write to out of range
> > > > > >   arm64: errata: Enable workaround for TRBE overwrite in FILL mode
> > > > > >   arm64: errata: Enable TRBE workaround for write to out-of-range
> > > > > >     address
> > > > > > 
> > > > > >  Documentation/arm64/silicon-errata.rst       |  12 +
> > > > > >  arch/arm64/Kconfig                           | 111 ++++++
> > > > > >  arch/arm64/include/asm/barrier.h             |  16 +-
> > > > > >  arch/arm64/include/asm/cputype.h             |   4 +
> > > > > >  arch/arm64/kernel/cpu_errata.c               |  64 +++
> > > > > >  arch/arm64/tools/cpucaps                     |   3 +
> > > > > >  drivers/hwtracing/coresight/coresight-trbe.c | 394 +++++++++++++++++--
> > > > > >  7 files changed, 567 insertions(+), 37 deletions(-)
> > > > > 
> > > > > I have applied this set.
> > > > 
> > > > Mathieu -- the plan here (which we have discussed on the list [1]) is
> > > > for the first four patches to be shared with arm64. Since you've gone
> > > > ahead and applied the whole series, please can you provide me a stable
> > > > branch with the first four patches only so that I can include them in
> > > > the arm64 tree?
> > > > 
> > > > Failing that, I can create a branch for you to pull and apply the remaining
> > > > patches on top.
> > > > 
> > > > Please let me know.
> > > 
> > > Coresight patches flow through Greg's tree and as such the coresight-next tree
> > > gets rebased anyway.  I will remove the first 4 patches and push again.  By the
> > > way do you also want to pick up patches 14 and 16 since they are concerned with
> > > "arch/arm64/Kconfig" or should I keep them?
> > 
> > I'll take the first 4 and put them on a stable branch, which you can choose
> > to pull if you like (but please don't rebase it or we'll end up with
> > duplicate commits). The rest of the patches, including the later Kconfig
> > changes, are yours but I doubt they'll apply cleanly without the initial
> > changes.
> > 
> > Are you sure Greg rebases everything? That sounds a bit weird to me, as it
> > means it's impossible to share branches with other trees. How do you usually
> > handle this situation?
> 
> No, I never rebase my trees.  For coresight patches I take them as
> emailed patches due to previous history requiring me to review them all
> myself.  If this is an issue here, I can always take a pull request as
> long as you all don't want my review :)

Can you expand on the "previous history requiring" you to review coresight
patches?

Rebasing the coresight-next tree when patches are pulled in the char-misc tree
causes problems when features involve other subsystems.  I definitely appreciate
reviews of coresight patches from anyone. The subsystem has grown to be very
complex and more reviewers mean higher probabilities of catching problems.
There has to be a way for that to continue while making it easier to collaborate
with other subsystems.

For this particular patchset, Will has picked up the first 4 patches, I will pick up
patches 5 to 13 and patches 14 and 15 will have to go in the next cycle.  I
doubt this is the best we can do.

Regards,
Mathieu

> 
> thanks,
> 
> greg k-h