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

[Serge Semin]

On Wed, Aug 31, 2022 at 09:36:46AM +0100, 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.

No. dw-edma-pcie has nothing to do with this driver.

-Sergey

> 
> Thanks,
> Robin.