linux-kernel - Re: [PATCH 2/2] arm64: tegra: Mark BPMP channels as no-memory-wc

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Message-ID: <20220623093606.GA181983@suse.de>
Date:   Thu, 23 Jun 2022 11:36:06 +0200
From:   Yousaf Kaukab <ykaukab@...e.de>
To:     Mikko Perttunen <cyndis@...si.fi>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mikko Perttunen <mperttunen@...dia.com>,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: tegra: Mark BPMP channels as no-memory-wc

On Wed, Jun 22, 2022 at 04:29:03PM +0300, Mikko Perttunen wrote:
> On 22.6.2022 16.23, Mikko Perttunen wrote:
> > From: Mikko Perttunen <mperttunen@...dia.com>
> > 
> > The Tegra SYSRAM contains regions access to which is restricted to
> > certain hardware blocks on the system, and speculative accesses to
> > those will cause issues.
> > 
> > Patch 'misc: sram: Only map reserved areas in Tegra SYSRAM' attempted
> > to resolve this by only mapping the regions specified in the device
> > tree on the assumption that there are no such restricted areas within
> > the 64K-aligned area of memory that contains the memory we wish to map.
> > 
> > Turns out this assumption is wrong, as there are such areas above the
> > 4K pages described in the device trees. As such, we need to use the
> > bigger hammer that is no-memory-wc, which causes the memory to be
> > mapped as Device memory to which speculative accesses are disallowed.
> > 
> > As such, the previous patch in the series,
> >    'firmware: tegra: bpmp: do only aligned access to IPC memory area',
> > is required with this patch to make the BPMP driver only issue aligned
> > memory accesses as those are also required with Device memory.
> > 
> > Fixes: fec29bf04994 ("misc: sram: Only map reserved areas in Tegra SYSRAM")
> > Signed-off-by: Mikko Perttunen <mperttunen@...dia.com>
> > ---
> 
> FWIW, with this, the aforementioned patch to misc/sram is redundant. It
> doesn't hurt, but doesn't really help either. Whether or not it should be
> reverted, I have no opinion.
I am in favor of reverting commit fec29bf04994 ("misc: sram: Only map
reserved areas in Tegra SYSRAM"). Tegra platforms are the only consumer
of this code. I consider it to be redundant after your series.
For both patches:
Reviewed-by: Yousaf Kaukab <ykaukab@...e.de>
> 
> Thanks,
> Mikko
BR,
Yousaf