Re: [PATCH v3 7/9] arm64: dts: renesas: rzg3s-smarc-som: Update dma-ranges for PCIe

[Claudiu Beznea]

Hi, Biju,

On 09.07.2025 08:05, Biju Das wrote:
> Hi Claudiu Beznea,
> 
>> -----Original Message-----
>> From: Claudiu Beznea <claudiu.beznea@xxxxxxxxx>
>> Sent: 08 July 2025 11:10
>> Subject: Re: [PATCH v3 7/9] arm64: dts: renesas: rzg3s-smarc-som: Update dma-ranges for PCIe
>>
>> Hi, Biju,
>>
>> On 07.07.2025 11:18, Biju Das wrote:
>>> Hi Claudiu,
>>>
>>>> -----Original Message-----
>>>> From: Claudiu <claudiu.beznea@xxxxxxxxx>
>>>> Sent: 04 July 2025 17:14
>>>> Subject: [PATCH v3 7/9] arm64: dts: renesas: rzg3s-smarc-som: Update
>>>> dma-ranges for PCIe
>>>>
>>>> From: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
>>>>
>>>> The first 128MB of memory is reserved on this board for secure area.
>>>> Update the PCIe dma-ranges property to reflect this.
>>>
>>> I see R-Car PCIe dma-ranges[1] and [2] maps all possible DDR area supported by the SoC?
>>> Do we need to make board specific as well there?
>>
>> I'm not familiar with R-Car, but if there are ranges reserved for other purposes, I think we should
>> reflect it in board specific device trees.
> 
> 
> Already Linux has this DDR info[1]. Linux provides DMA memory only from this region.

What we provide though dma-ranges DT property is setup in the PCI
controller register corresponding to the AXI windows. It is the same in
case of R-Car (as of my investigation on driver).

> 
> In your testing, have you faced any issue like system allocated DMA region other than [1]
> and you don't want to use it, then the changes are ok??

I haven't currently encounter any issues.

As the values passed though the dma-ranges DT property are setup in the
controller register for AXI windows, and the DMA endpoints can act as bus
masters, to avoid any issue where the DMA endpoints may corrupt memory
specific to the secure area, I chose to update the "dma-ranges" though
board specific bindings (to reflect the presence of the secure area and
tell the PCIe controller to not use it).

> 
> Not sure, PCIe can work on internal memory such as SRAM?

Inbound window is RAM, outbound window is a PCIe specific memory described
though "ranges" DT property.

Thank you for your review,
Claudiu

> 
> [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/arch/arm64/boot/dts/renesas/rzg3s-smarc-som.dtsi?h=next-20250708#n31
> 
> Cheers,
> Biju