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SubjectRe: [PATCH v5 20/20] PCI: dwc: Add Baikal-T1 PCIe controller support
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On 2022-08-29 16:28, Lorenzo Pieralisi wrote:
[...]
>> +static int bt1_pcie_add_port(struct bt1_pcie *btpci)
>> +{
>> + struct device *dev = &btpci->pdev->dev;
>> + int ret;
>> +
>> + /*
>> + * DW PCIe Root Port controller is equipped with eDMA capable of
>> + * working with the 64-bit memory addresses.
>> + */
>> + ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64));
>> + if (ret)
>> + return ret;
>
> Is this the right place to set the DMA mask for the host controller
> embedded DMA controller (actually, the dev pointer is the _host_
> controller device) ?
>
> How this is going to play when combined with:
>
> https://lore.kernel.org/linux-pci/1e63a581-14ae-b4b5-a5bf-ca8f09c33af6@arm.com
>
> It is getting a bit confusing. I believe the code in the link
> above sets the mask so that through the DMA API we are capable
> of getting an MSI doorbell virtual address whose physical address
> can be addressed by the endpoint; this through the DMA API.
>
> This patch is setting the DMA mask for a different reason, namely
> setting the host controller embedded DMA controller addressing
> capabilities.
>
> AFAICS - both approaches set the mask for the same device - now
> the question is about which one is legitimate and how to handle
> the other.

Assuming the dw-edma-pcie driver is the relevant one, that already sets
its own masks on its own device, so I also don't see why this is here.

Thanks,
Robin.

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