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

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Message-ID: <640775cb-3508-4228-aa94-2e4b7b6b2b6d@linaro.org>
Date: Sat, 24 Feb 2024 01:07:26 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Mrinmay Sarkar <quic_msarkar@...cinc.com>, 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 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