Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <6a5b523d-711b-d809-06b9-fdada64c9c65@leemhuis.info>
Date:   Mon, 28 Nov 2022 06:44:13 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.4.1
Subject: Re: [PATCH] Revert "arm64: dma: Drop cache invalidation from
 arch_dma_prep_coherent()"
Content-Language: en-US, de-DE
To:     Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        catalin.marinas@arm.com, will@kernel.org
Cc:     robin.murphy@arm.com, amit.pundir@linaro.org, andersson@kernel.org,
        quic_sibis@quicinc.com, sumit.semwal@linaro.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20221114110329.68413-1-manivannan.sadhasivam@linaro.org>
From:   Thorsten Leemhuis <regressions@leemhuis.info>
In-Reply-To: <20221114110329.68413-1-manivannan.sadhasivam@linaro.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 14.11.22 12:03, Manivannan Sadhasivam wrote:
> This reverts commit c44094eee32f32f175aadc0efcac449d99b1bbf7.
> 
> As reported by Amit [1], dropping cache invalidation from
> arch_dma_prep_coherent() triggers a crash on the Qualcomm SM8250 platform
> (most probably on other Qcom platforms too). The reason is, Qcom
> qcom_q6v5_mss driver copies the firmware metadata and shares it with modem
> for validation. The modem has a secure block (XPU) that will trigger a
> whole system crash if the shared memory is accessed by the CPU while modem
> is poking at it.
> [...]
> [1] https://lore.kernel.org/linux-arm-kernel/CAMi1Hd1VBCFhf7+EXWHQWcGy4k=tcyLa7RGiFdprtRnegSG0Mw@mail.gmail.com/
>

I have Amit's report on the list of tracked regressions. I also noticed
the proposed change "arm64: dts: qcom: sc8280xp: fix PCIe DMA coherency":
https://lore.kernel.org/all/20221124142501.29314-1-johan+linaro@kernel.org/

I have no expertise in this area, but it looked somewhat related to my
eyes, so please allow me to quickly ask: is that related or even
supposed to fix Amit's regression?

Ciao, Thorsten