Re: [PATCH v3] PCI: rcar-gen4: Limit Max_Read_Request_Size and Max_Payload_Size to 256 Bytes

[Manivannan Sadhasivam]

On Fri, 21 Aug 2026 04:05:51 +0200, Marek Vasut wrote:
> R-Car Gen4 PCIe controller has a hardware limitation of 256 Bytes
> Max_Payload_Size (MPS). PCIe specification indicates that the MPS
> must not exceed minimum MPS of any element along the packet path.
> Force limit Max_Payload_Size to at most 256 Bytes for each device
> connected to this PCIe controller.
> 
> R-Car Gen4 Reference Manual, chapter 104.4.8 Usage notes for
> MRRS (Max Read Request Size) states:
>   Please set "Max Read Request Size" to 128 bytes or 256 bytes.
>   If "Max Read Request Size" is set to anything other than the
>   above, the transferred data will not match the expected value.
> This limitation also seems the apply to devices issuing MRd TLP.
> This limitation can be triggered by using non-HMB NVMe SSD with
> Max_Read_Request_Size 512 Bytes, for example Crucial P5 Plus.
> Any write into the SSD (MRd TLP issued by the SSD) longer than
> 256 Bytes wraps around at 256 Byte boundary, and the same data
> are written into the SSD starting at offset 0 and at 256 Bytes.
> Force limit Max_Read_Request_Size to at most 256 Bytes for each
> device connected to this PCIe controller to avoid this behavior.
> 
> [...]

Applied, thanks!

[1/1] PCI: rcar-gen4: Limit Max_Read_Request_Size and Max_Payload_Size to 256 Bytes
      commit: d1f8ada0815e247b52e5f9d4ff3a8bc9e4080bb9

Best regards,
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