Re: [PATCH v3] ata: sata_rcar: Fix DMA boundary mask

[Sergei Shtylyov]

On 10/16/20 7:40 PM, Andy Shevchenko wrote:

>> 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.
>>
>> This also fixes the following WRITE DMA EXT timeout issue:
>>
>>     # dd if=/dev/urandom of=/mnt/de1/file1-1024M bs=1M count=1024
>>     ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
>>     ata1.00: failed command: WRITE DMA EXT
>>     ata1.00: cmd 35/00:00:00:e6:0c/00:0a:00:00:00/e0 tag 0 dma 1310720 out
>>     res 40/00:01:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
>>     ata1.00: status: { DRDY }
>>
>> as seen by Shimoda-san since commit 429120f3df2dba2b ("block: fix
>> splitting segments on boundary masks").
>>
>> Fixes: 8bfbeed58665dbbf ("sata_rcar: correct 'sata_rcar_sht'")
>> Fixes: 9495b7e92f716ab2 ("driver core: platform: Initialize dma_parms for platform devices")
>> Fixes: 429120f3df2dba2b ("block: fix splitting segments on boundary masks")
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
>> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
>> Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> Reviewed-by: Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx>
>> Reviewed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
>> Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
>> Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
>> Cc: stable <stable@xxxxxxxxxxxxxxx>
>> ---
>> v3:
>>   - Add Reviewed-by, Tested-by,
>>   - Augment description and Fixes: with Shimoda-san's problem report
>>     https://lore.kernel.org/r/1600255098-21411-1-git-send-email-yoshihiro.shimoda.uh@xxxxxxxxxxx,
>>
>> v2:
>>   - Add Reviewed-by, Tested-by, Cc.
>> ---
>>  drivers/ata/sata_rcar.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/ata/sata_rcar.c b/drivers/ata/sata_rcar.c
>> index 141ac600b64c87ef..44b0ed8f6bb8a120 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_DTEND                        BIT(0)
>>
>> -#define SATA_RCAR_DMA_BOUNDARY         0x1FFFFFFEUL
>> +#define SATA_RCAR_DMA_BOUNDARY         0x1FFFFFFFUL
> 
> Wondering if GENMASK() here will be better to avoid such mistakes.

   How? The bit 0 is reserved, so only even byte counts are possiblе...

[...]

MBR, Sergei