Re: [PATCH] Revert "arm64: dma: Drop cache invalidation from arch_dma_prep_coherent()"

From: Amit Pundir <amit.pundir@linaro.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Thorsten Leemhuis <regressions@leemhuis.info>,
	Sibi Sankar <quic_sibis@quicinc.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
	Will Deacon <will@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	andersson@kernel.org, sumit.semwal@linaro.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Revert "arm64: dma: Drop cache invalidation from arch_dma_prep_coherent()"
Date: Fri, 2 Dec 2022 13:56:03 +0530	[thread overview]
Message-ID: <CAMi1Hd2wM5MLsjkx0HAWKkswzTDACb0C4tsPymNrRa0ariWsww@mail.gmail.com> (raw)
In-Reply-To: <Y4joR2sQMMjIt+yE@arm.com>

On Thu, 1 Dec 2022 at 23:15, Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Thu, Dec 01, 2022 at 10:29:39AM +0100, Thorsten Leemhuis wrote:
> > Has any progress been made to fix this regression? It afaics is not a
> > release critical issue, but well, it still would be nice to get this
> > fixed before 6.1 is released.
>
> The only (nearly) risk-free "fix" for 6.1 would be to revert the commit
> that exposed the driver bug. It doesn't fix the actual bug, it only
> makes it less likely to happen.
>
> I like the original commit removing the cache invalidation as it shows
> drivers not behaving properly but, as a workaround, we could add a
> command line option to force back the old behaviour (defaulting to the
> new one) until the driver is fixed.

We use DB845c extensively for mainline and android-mainline[1] testing
with AOSP, and it is broken for weeks now. So be it a temporary
workaround or a proper driver fix in place, we'd really appreciate a
quick fix here.

I understand that the revert doesn't fix the actual driver bug, but we
were very very lucky so far that we had never hit this issue before.
So at this point I'll take the revert of the upstream commit as well,
while a proper fix is being worked upon.

Regards,
Amit Pundir
[1] https://android.googlesource.com/kernel/common/+/refs/heads/android-mainline

>
> --
> Catalin