On Tue, Mar 26, 2024 at 12:05:42PM +0100, Niklas Cassel wrote: > On Tue, Mar 26, 2024 at 01:56:36PM +0530, Manivannan Sadhasivam wrote: > > On Fri, Mar 22, 2024 at 05:10:06PM +0100, Niklas Cassel wrote: > > > On Thu, Mar 14, 2024 at 08:53:44PM +0530, Manivannan Sadhasivam wrote: > > > > To maintain uniformity across EPF drivers, let's move the DMA > > > > initialization to EPC init callback. This will also allow us to deinit DMA > > > > during PERST# assert in the further commits. > > > > > > > > For EPC drivers without PERST#, DMA deinit will only happen during driver > > > > unbind. > > > > > > > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx> > > > > --- > > > > > > Reviewed-by: Niklas Cassel <cassel@xxxxxxxxxx> > > > > > > > > > For the record, I was debugging a problem related to EPF DMA recently > > > and was dumping the DMA mask for the struct device of the epf driver. > > > I was a bit confused to see it as 32-bits, even though the EPC driver > > > has it set to 64-bits. > > > > > > The current code works, because e.g., pci_epf_test_write(), etc, > > > does: > > > struct device *dma_dev = epf->epc->dev.parent; > > > dma_map_single(dma_dev, ...); > > > > > > but it also means that all EPF drivers will do this uglyness. > > > > > > > This ugliness is required as long as the dmaengine is associated only with the > > EPC. > > > > > > > > > > > However, if a EPF driver does e.g. > > > dma_alloc_coherent(), and sends in the struct *device for the EPF, > > > which is the most logical thing to do IMO, it will use the wrong DMA > > > mask. > > > > > > Perhaps EPF or EPC code should make sure that the struct *device > > > for the EPF will get the same DMA mask as epf->epc->dev.parent, > > > so that EPF driver developer can use the struct *epf when calling > > > e.g. dma_alloc_coherent(). > > > > > > > Makes sense. I think it can be done during bind() in the EPC core. Feel free to > > submit a patch if you like, otherwise I'll keep it in my todo list. > > So we still want to test: > -DMA API using the eDMA > -DMA API using the "dummy" memcpy dma-channel. > > However, it seems like both pci-epf-mhi.c and pci-epf-test.c > do either: > -Use DMA API > or > -Use memcpy_fromio()/memcpy_toio() instead of DMA API > > > To me, it seems like we should always be able to use > DMA API (using either a eDMA or "dummy" memcpy). > > I don't really see the need to have the path that does: > memcpy_fromio()/memcpy_toio(). > > I know that for DWC, when using memcpy (and this also > memcpy via DMA API), we need to map the address using > iATU first. > > But that could probably be done using another flag, > perhaps rename that flag FLAG_USE_DMA to NEEDS_MAP or > something. > (Such that we can change these drivers to only have a > code path that uses DMA API.) Looking at pci-epf-mhi.c, it seems to use names like: pci_epf_mhi_iatu_read() and pci_epf_mhi_edma_read(). This seems to be a very DWC focused naming. AFAICT, EPF drivers should work on any PCIe EP controller that implements the EPC API. Yes, I understand that it is only Qualcomm that uses this MHI interface/bus, but what is stopping Qualcomm from using a non-DWC based PCIe EP controller in an upcoming SoC? Surely that Qualcomm SoC could still implement the MHI interface/bus, so perhaps the naming in this EPF driver should use somewhat less "EPC vendor specific" function names? Kind regards, Niklas
