Re: [PATCH v7 23/25] PCI: dwc: Restore DMA-mask after MSI-data allocation
From: Robin Murphy
Date: Fri Dec 16 2022 - 09:01:44 EST
On 2022-12-16 10:18, Serge Semin wrote:
On Fri, Dec 16, 2022 at 01:49:38AM -0800, Christoph Hellwig wrote:
On Fri, Dec 16, 2022 at 12:34:23PM +0300, Serge Semin wrote:
What about instead of save/restore pattern I'll just change the
dma_set_mask_and_coherent() method with the dma_set_coherent_mask()
function call? It seems cleaner. Like this:
Thus the platform-specific streaming DMA mask would be preserved.
Since it's PCIe then having the streaming DMA-mask less than 32-bits
wide is very much improbable. Moreover DW PCIe AXI-interface can be
synthesize only with one out of two address bus widths: 32 and 64.
Where platform-specific means the dwc subdriver?
Right. I meant the streaming DMA-mask set by the low-level DWC PCIe drivers
(like pcie-qcom(-ep)?.c, pcie-bt1.c, etc). It's very much important to
have the real DMA-mask (at least the streaming one) set for the eDMA-capable
controllers so the DMA-engine clients would work with the best performance.
Yes, that seems to work.
Ok. I'll just use the direct dma_set_coherent_mask() method here then.
Alternatively have a flag that says which streaming mask
to set.
I'd prefer to have more flexibility here relying on the low-level
drivers to set the mask(s) instead of adding the new flag, just in case
if there is vendor-specific IP-core/platform changes in the address
bus width.
Presumably the low-level glue drivers could pass a bus size or mask
value in struct dw_pcie_rp/dw_pcie, so the actual dma_set_mask() call
itself could be centralised? I guess there's also an argument that only
glue drivers which care about eDMA need to care about setting a mask at
all, so I don't have a string preference either way. If you'd rather
stick with that approach then it might be worth a brief comment at each
site to clarify why the other mask is being set from an entirely
different place, just in case anyone comes along and tries to "fix" it.
Cheers,
Robin.