RE: [PATCH] ata: sata_rcar: Fix DMA boundary mask

Hi Geert,

Thank you for the patch.

-----Original Message-----
From: linux-ide-owner@vger.kernel.org <redacted> On Behalf Of Geert Uytterhoeven <geert+renesas@glider.be>
Sent: 13 May 2020 12:04
To: Jens Axboe <axboe@kernel.dk>; Ulf Hansson <redacted>; Greg Kroah-Hartman <gregkh@linuxfoundation.org>;
Christoph Hellwig [off-list ref]
Cc: Sergei Shtylyov <redacted>; linux-ide@vger.kernel.org; linux-renesas-soc@vger.kernel.org; linux-
scsi@vger.kernel.org; linux-kernel@vger.kernel.org; Geert Uytterhoeven [off-list ref]
Subject: [PATCH] ata: sata_rcar: Fix DMA boundary mask

Before commit 9495b7e92f716ab2 ("driver core: platform: Initialize
dma_parms for platform devices"), the R-Car SATA device didn't have DMA
parameters.  Hence the DMA boundary mask supplied by its driver was
silently ignored, as __scsi_init_queue() doesn't check the return value
of dma_set_seg_boundary(), and the default value of 0xffffffff was used.

Now the device has gained DMA parameters, the driver-supplied value is
used, and the following warning is printed on Salvator-XS:

    DMA-API: sata_rcar ee300000.sata: mapping sg segment across boundary [start=0x00000000ffffe000] [end=0x00000000ffffefff]
[boundary=0x000000001ffffffe]
    WARNING: CPU: 5 PID: 38 at kernel/dma/debug.c:1233 debug_dma_map_sg+0x298/0x300

(the range of start/end values depend on whether IOMMU support is
 enabled or not)

The issue here is that SATA_RCAR_DMA_BOUNDARY doesn't have bit 0 set, so
any typical end value, which is odd, will trigger the check.

Fix this by increasing the DMA boundary value by 1.

Fixes: 8bfbeed58665dbbf ("sata_rcar: correct 'sata_rcar_sht'")
Fixes: 9495b7e92f716ab2 ("driver core: platform: Initialize dma_parms for platform devices")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
As by default the DMA debug code prints the first error only, this issue
may be hidden on plain v5.7-rc5, where the FCP driver triggers a similar
warning.  Merging commit dd844fb8e50b12e6 ("media: platform: fcp: Set
appropriate DMA parameters") from the media tree fixes the FCP issue,
and exposes the SATA issue.

I added the second fixes tag because that commit is already being
backported to stable kernels, and this patch thus needs backporting,
too.
---
 drivers/ata/sata_rcar.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Without this patch I see SATA link being reset while doing a dd (dd if=/dev/urandom of=random-data bs=1M count=1000)

Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>

Cheers,
Prabhakar

quoted hunk

diff --git a/drivers/ata/sata_rcar.c b/drivers/ata/sata_rcar.c
index 980aacdbcf3b42b9..752db75b611e8f8a 100644
--- a/drivers/ata/sata_rcar.c
+++ b/drivers/ata/sata_rcar.c

@@ -120,7 +120,7 @@
 /* Descriptor table word 0 bit (when DTA32M = 1) */
 #define SATA_RCAR_DTENDBIT(0)

-#define SATA_RCAR_DMA_BOUNDARY0x1FFFFFFEUL
+#define SATA_RCAR_DMA_BOUNDARY0x1FFFFFFFUL

 /* Gen2 Physical Layer Control Registers */
 #define RCAR_GEN2_PHY_CTL1_REG0x1704
--

2.17.1

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