On Wed, May 22, 2024 at 11:12:43AM -0400, Nícolas F. R. A. Prado wrote: > On Wed, May 22, 2024 at 05:24:40PM +0300, Andy Shevchenko wrote: > > On Wed, May 22, 2024 at 03:18:18PM +0200, Neil Armstrong wrote: > > > On 22/05/2024 13:53, Neil Armstrong wrote: > > > > On 22/05/2024 13:33, Andy Shevchenko wrote: > > > > > On Wed, May 22, 2024 at 12:03:33PM +0200, Neil Armstrong wrote: > > > > > > On 15/05/2024 23:09, Nícolas F. R. A. Prado wrote: > > > > > > > On Tue, May 07, 2024 at 11:10:27PM +0300, Andy Shevchenko wrote: > > > > > > > > Both dma_unmap_sgtable() and sg_free_table() in spi_unmap_buf_attrs() > > > > > > > > have checks for orig_nents against 0. No need to duplicate this. > > > > > > > > All the same applies to other DMA mapping API calls. > > > > > > > > > > > > > > > > Also note, there is no other user in the kernel that does this kind of > > > > > > > > checks. > > > > > > > > > > > > > > > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > > > > > > > > > > > > > > Hi, > > > > > > > > > > > > > > this commit caused a regression which I reported here: > > > > > > > > > > > > > > https://lore.kernel.org/all/d3679496-2e4e-4a7c-97ed-f193bd53af1d@notapiano > > > > > > > > > > > > > > along with some thoughts on the cause and a possible solution, though I'm not > > > > > > > familiar with this code base at all and would really appreciate any feedback you > > > > > > > may have. > > > > > > > > > > > > I also see the same regression on the SM8550 and SM8650 platforms, > > > > > > please CC linux-arm-msm@xxxxxxxxxxxxxxx and me for a potential fix to test on those platforms. > > > > > > > > > > There is still no answer from IOMMU patch author. Do you have the same trace > > > > > due to IOMMU calls? Anyway, I guess it would be nice to see it. > [..] > > > > > > > > > > Meanwhile, I have three changes I posted in the replies to the initial report, > > > > > can you combine them all and test? This will be a plan B (? or A, depending on > > > > > the culprit). > > > > > > > > > > > > > I'll try to apply them and test. > > > > > > I stacked the 3 changes, and it works: > > > Tested-by: Neil Armstrong <neil.armstrong@xxxxxxxxxx> # on SM8650-QRD > > > > Thank you! > > > > I will try to develop and submit a fix against IOMMU which I believe is the > > correct place to address this. So, this one will be plan B in case the IOMMU > > folks will refuse the other one. > > Hi, > > that change did not work for me. Stack trace follows at the end. > > But adding the following on top did fix it: > > diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c > index 0851c5e1fd1f..5d3972d9d1da 100644 > --- a/drivers/spi/spi.c > +++ b/drivers/spi/spi.c > @@ -1253,8 +1253,13 @@ static int __spi_map_msg(struct spi_controller *ctlr, struct spi_message *msg) > /* The sync is done before each transfer. */ > unsigned long attrs = DMA_ATTR_SKIP_CPU_SYNC; > > - if (!ctlr->can_dma(ctlr, msg->spi, xfer)) > + if (!ctlr->can_dma(ctlr, msg->spi, xfer)) { > + memset(&xfer->tx_sg, 0, sizeof(xfer->tx_sg)); > + xfer->tx_sg.sgl = &dummy_sg; > + memset(&xfer->rx_sg, 0, sizeof(xfer->rx_sg)); > + xfer->rx_sg.sgl = &dummy_sg; > continue; > + } > > if (xfer->tx_buf != NULL) { > ret = spi_map_buf_attrs(ctlr, tx_dev, &xfer->tx_sg, > > > The thing is that even with all the previous changes applied, if one of the > transfers inside the message doesn't support DMA, the null pointer would still > be passed to the DMA API. Ah, indeed, the conditionals also can be translated to can_dma = can_dma(); if (can_dma && _buf) ... else ... but... > Alternatively, I think a better way to achieve the same is (I have verified this > also works): I agree that this one is much better approach. I will clean it up and send as a quick fix. IOMMU will still be on the table as I think it's wrong to dereference SG when nents = 0. > I'll let you decide what is the best fix for the issue (what has been posted so > far in this thread or another fix in IOMMU). If you go with this, feel free to > add my > > Tested-by: Nícolas F. R. A. Prado <nfraprado@xxxxxxxxxxxxx> Thank you! -- With Best Regards, Andy Shevchenko
