linux-kernel - Re: [PATCH v1 1/1] spi: Remove unneded check for orig

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Date: Thu, 16 May 2024 16:25:35 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Nícolas F. R. A. Prado <nfraprado@...labora.com>
Cc: Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] spi: Remove unneded check for orig_nents

On Thu, May 16, 2024 at 01:18:04PM +0300, Andy Shevchenko wrote:
> On Wed, May 15, 2024 at 05:09:33PM -0400, 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@...ux.intel.com>
> > 
> > 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.
> 
> Thanks for the report and preliminary analysis!
> I'll look at it hopefully sooner than later.
> 
> But at least what I think now is that my change revealed a problem somewhere
> else, because that's how DMA mapping / streaming APIs designed, it's extremely
> rare to check orig_nents field.

Can you test the below patch?

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index b2efd4964f7c..51811f04e463 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1243,6 +1243,7 @@ static int __spi_map_msg(struct spi_controller *ctlr, struct spi_message *msg)
 	else
 		rx_dev = ctlr->dev.parent;
 
+	ret = -ENOMSG;
 	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
 		/* The sync is done before each transfer. */
 		unsigned long attrs = DMA_ATTR_SKIP_CPU_SYNC;
@@ -1272,6 +1273,9 @@ static int __spi_map_msg(struct spi_controller *ctlr, struct spi_message *msg)
 			}
 		}
 	}
+	/* No transfer has been mapped, bail out with success */
+	if (ret)
+		return 0;
 
 	ctlr->cur_rx_dma_dev = rx_dev;
 	ctlr->cur_tx_dma_dev = tx_dev;


If it fixes the issue, I will submit it properly.

-- 
With Best Regards,
Andy Shevchenko