linux-kernel - Re: [PATCH v4] iommu/arm-smmu-qcom: Limit the SMR groups to 128

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Message-ID: <ZBmL+FW44VjxycaA@hovoldconsulting.com>
Date:   Tue, 21 Mar 2023 11:50:32 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     will@...nel.org, joro@...tes.org, robin.murphy@....com,
        andersson@...nel.org, johan+linaro@...nel.org, steev@...i.org,
        linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] iommu/arm-smmu-qcom: Limit the SMR groups to 128

On Tue, Mar 21, 2023 at 02:43:32PM +0530, Manivannan Sadhasivam wrote:
> On some Qualcomm platforms, the hypervisor emulates more than 128 SMR
> (Stream Matching Register) groups. This doesn't conform to the ARM SMMU
> architecture specification which defines the range of 0-127. Moreover, the
> emulated groups don't exhibit the same behavior as the architecture
> supported ones.
> 
> For instance, emulated groups will not detect the quirky behavior of some
> firmware versions intercepting writes to S2CR register, thus skipping the
> quirk implemented in the driver and causing boot crash.
> 
> So let's limit the groups to 128 and issue a notice to users in that case.
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Reviewed-by: Johan Hovold <johan+linaro@...nel.org>
Tested-by: Johan Hovold <johan+linaro@...nel.org>

Johan