linux-kernel - Re: [PATCH v2] misc: sram: Only map reserved areas in Tegra SYSRAM

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Date:   Wed, 21 Jul 2021 16:08:17 +0200
From:   Mian Yousaf Kaukab <ykaukab@...e.de>
To:     Mikko Perttunen <mperttunen@...dia.com>
Cc:     arnd@...db.de, gregkh@...uxfoundation.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] misc: sram: Only map reserved areas in Tegra SYSRAM

On Thu, Jul 15, 2021 at 01:34:23PM +0300, Mikko Perttunen wrote:
> On Tegra186 and later, a portion of the SYSRAM may be reserved for use
> by TZ. Non-TZ memory accesses to this portion, including speculative
> accesses, trigger SErrors that bring down the system. This does also
> happen in practice occasionally (due to speculative accesses).
> 
> To fix the issue, add a flag to the SRAM driver to only map the
> device tree-specified reserved areas depending on a flag set
> based on the compatibility string. This would not affect non-Tegra
> systems that rely on the entire thing being memory mapped.
> 
> If 64K pages are being used, we cannot exactly map the 4K regions
> that are placed in SYSRAM - ioremap code instead aligns to closest
> 64K pages. However, since in practice the non-accessible memory area
> is 64K aligned, these mappings do not overlap with the non-accessible
> memory area and things work out.
> 
> Signed-off-by: Mikko Perttunen <mperttunen@...dia.com>

Reviewed-by: Mian Yousaf Kaukab <ykaukab@...e.de>