On Sat, 27 Jan 2024, Linus Walleij wrote: > Hi Nico! > > nice to mail with you as always! > > On Sat, Jan 27, 2024 at 4:51 AM Nicolas Pitre <nico@xxxxxxxxxxx> wrote: > > On Sat, 27 Jan 2024, Linus Walleij wrote: > > > > > Use the scatterlist memory iterator instead of just > > > dereferencing virtual memory using sg_virt(). > > > This make highmem references work properly. > > > > > > This driver also has a bug in the PIO sglist handling that > > > is fixed as part of the patch: it does not travers the > > > list of scatterbuffers: it will just process the first > > > item in the list. This is fixed by augmenting the logic > > > such that we do not process more than one sgitem > > > per IRQ instead of counting down potentially the whole > > > length of the request. > > > > > > We can suspect that the PIO path is quite untested. > > > > It was tested for sure ... at least by myself ... some 17 years ago ! > > Hm, on the DMA path the code is taking struct mmc_data .sg_len > into account but not on the polled I/O path. > > But I think sg_len is very often 1, as long as the memory isn't very > fragmented so pieces of a file you read/write are all over the place. > > It needs to be tested under high memory pressure to provoke errors > I think. I'm not sure, the block layer people may have some secret > testing trick! (I actually have this hardware in a Kirkwood NAS.) Oh, I don't mean to imply that the testing was thorough. Especially given that, under normal circumstances, you're always using DMA with nicely aligned and sized blocks. But SDIO is different (smallish buffers). So the PIO support was added only to work around hw bugs in that case. Good you fixed it nevertheless. > > > if (!nodma) > > > - dev_dbg(host->dev, "fallback to PIO for data at 0x%p size %d\n", > > > - host->pio_ptr, host->pio_size); > > > + dev_dbg(host->dev, "fallback to PIO for data\n"); > > > > Given this message is about telling you why PIO is used despite not > > having asked for it, I think it would be nicer to preserve the > > equivalent info responsible for this infliction i.e. data->sg->offset > > and data->blksz. > > OK I fix! > > Yours, > Linus Walleij >
