Re: [PATCH v5 20/20] PCI: dwc: Add Baikal-T1 PCIe controller support

[Robin Murphy]

On 2022-08-31 09:36, Robin Murphy wrote:
> 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@xxxxxxx
> >
> > 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.

Ah, I just found the patch at [1], which further implies that this is 
indeed completely bogus.

Robin.

[1] 
https://lore.kernel.org/dmaengine/20220822185332.26149-23-Sergey.Semin@xxxxxxxxxxxxxxxxxxxx/