Re: [PATCH RESEND v5 24/24] PCI: dwc: Add DW eDMA engine support

[Bjorn Helgaas]

On Wed, Aug 24, 2022 at 09:13:19PM +0300, Serge Semin wrote:
> On Wed, Aug 24, 2022 at 11:51:18AM -0500, Bjorn Helgaas wrote:
> > On Mon, Aug 22, 2022 at 09:53:32PM +0300, Serge Semin wrote:

> > > +	val = dw_pcie_readl_dbi(pci, PCIE_DMA_VIEWPORT_BASE + PCIE_DMA_CTRL);
> > > +	if (val == 0xFFFFFFFF && pci->edma.reg_base) {
> > > +		pci->edma.mf = EDMA_MF_EDMA_UNROLL;
> > > +
> > > +		val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
> > > +	} else if (val != 0xFFFFFFFF) {
> > 
> 
> > Consider PCI_POSSIBLE_ERROR() as an annotation about the meaning of
> > 0xFFFFFFFF and something to grep for.
> 
> In this case FFs don't mean an error but a special value, which
> indicates that the eDMA is mapped via the unrolled CSRs space. The
> similar approach has been implemented for the iATU legacy/unroll setup
> auto-detection. So I don't see much reasons to have it grepped, so as
> to have a macro-based parametrization since the special value will
> unluckily change while having the explicit literal utilized gives a
> better understanding of the way the algorithm works.

If 0xFFFFFFFF is the result of a successful PCIe Memory Read, and not
something synthesized by the host bridge when it handles an
Unsupported Request completion, I'm fine with keeping it as is.