linux-kernel - Re: [PATCH v5 0/3] arm64: qcom: sa8775p: add cache coherency support for SA8775P

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Date: Wed, 28 Feb 2024 15:02:11 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Mrinmay Sarkar <quic_msarkar@...cinc.com>, andersson@...nel.org,
 krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
 konrad.dybcio@...aro.org, manivannan.sadhasivam@...aro.org, robh@...nel.org
Cc: quic_shazhuss@...cinc.com, quic_nitegupt@...cinc.com,
 quic_ramkri@...cinc.com, quic_nayiluri@...cinc.com,
 dmitry.baryshkov@...aro.org, quic_krichai@...cinc.com,
 quic_vbadigan@...cinc.com, quic_schintav@...cinc.com,
 Lorenzo Pieralisi <lpieralisi@...nel.org>,
 Krzysztof Wilczyński <kw@...ux.com>,
 Bjorn Helgaas <bhelgaas@...gle.com>, linux-arm-msm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-pci@...r.kernel.org
Subject: Re: [PATCH v5 0/3] arm64: qcom: sa8775p: add cache coherency support
 for SA8775P

On 28/02/2024 14:07, Mrinmay Sarkar wrote:
> 
> On 2/24/2024 3:49 PM, Krzysztof Kozlowski wrote:
>> On 23/02/2024 15:03, Mrinmay Sarkar wrote:
>>> Due to some hardware changes, SA8775P has set the NO_SNOOP attribute
>>> in its TLP for all the PCIe controllers. NO_SNOOP attribute when set,
>>> the requester is indicating that there no cache coherency issues exit
>>> for the addressed memory on the host i.e., memory is not cached. But
>>> in reality, requester cannot assume this unless there is a complete
>>> control/visibility over the addressed memory on the host.
>>>
>>> And worst case, if the memory is cached on the host, it may lead to
>>> memory corruption issues. It should be noted that the caching of memory
>>> on the host is not solely dependent on the NO_SNOOP attribute in TLP.
>>>
>>> So to avoid the corruption, this patch overrides the NO_SNOOP attribute
>>> by setting the PCIE_PARF_NO_SNOOP_OVERIDE register. This patch is not
>>> needed for other upstream supported platforms since they do not set
>>> NO_SNOOP attribute by default.
>>>
>>> This series is to enable cache snooping logic in both RC and EP driver
>>> and add the "dma-coherent" property in dtsi to support cache coherency
>>> in SA8775P platform.
>> Please confirm that your patchset passes 100% dtbs_check.
>>
>> Best regards,
>> Krzysztof
> 
> I have run dtbs_check and it is passing.

Hm, last time I checked dma-coherent was not allowed.

Best regards,
Krzysztof