linux-kernel - Re: [PATCH v5 2/3] PCI: qcom-ep: Enable cache coherency for SA8775P EP

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Message-ID: <8dc0f8e4-e7e6-98b6-037b-31b86c6087af@quicinc.com>
Date: Wed, 28 Feb 2024 18:36:01 +0530
From: Mrinmay Sarkar <quic_msarkar@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@...aro.org>, <andersson@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.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 2/3] PCI: qcom-ep: Enable cache coherency for SA8775P
 EP


On 2/24/2024 5:37 AM, Konrad Dybcio 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.
>>
>> Signed-off-by: Mrinmay Sarkar <quic_msarkar@...cinc.com>
>> ---
>>   drivers/pci/controller/dwc/pcie-qcom-ep.c | 20 +++++++++++++++++---
>>   1 file changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/pci/controller/dwc/pcie-qcom-ep.c b/drivers/pci/controller/dwc/pcie-qcom-ep.c
>> index 89d06a3e6e06..369954649254 100644
>> --- a/drivers/pci/controller/dwc/pcie-qcom-ep.c
>> +++ b/drivers/pci/controller/dwc/pcie-qcom-ep.c
>> @@ -45,6 +45,7 @@
>>   #define PARF_SLV_ADDR_MSB_CTRL			0x2c0
>>   #define PARF_DBI_BASE_ADDR			0x350
>>   #define PARF_DBI_BASE_ADDR_HI			0x354
>> +#define PARF_NO_SNOOP_OVERIDE			0x3d4
> Any reason for this to be unsorted?
>
> Konrad
Yes, this should be sorted. Will fix this in next series.

Thanks
Mrinmay