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SubjectRe: [PATCH v7 23/25] PCI: dwc: Restore DMA-mask after MSI-data allocation
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.


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