Pavel Machek wrote:
Clarify comment in sata_svw.c. Signed-off-by: Pavel Machek <pavel@xxxxxxx> diff --git a/drivers/ata/sata_svw.c b/drivers/ata/sata_svw.c index 16aa683..fb13b82 100644 --- a/drivers/ata/sata_svw.c +++ b/drivers/ata/sata_svw.c @@ -253,21 +253,29 @@ static void k2_bmdma_start_mmio(struct a /* start host DMA transaction */ dmactl = readb(mmio + ATA_DMA_CMD); writeb(dmactl | ATA_DMA_START, mmio + ATA_DMA_CMD); - /* There is a race condition in certain SATA controllers that can - be seen when the r/w command is given to the controller before the - host DMA is started. On a Read command, the controller would initiate - the command to the drive even before it sees the DMA start. When there - are very fast drives connected to the controller, or when the data request - hits in the drive cache, there is the possibility that the drive returns a part - or all of the requested data to the controller before the DMA start is issued. - In this case, the controller would become confused as to what to do with the data. - In the worst case when all the data is returned back to the controller, the - controller could hang. In other cases it could return partial data returning - in data corruption. This problem has been seen in PPC systems and can also appear - on an system with very fast disks, where the SATA controller is sitting behind a - number of bridges, and hence there is significant latency between the r/w command - and the start command. */ - /* issue r/w command if the access is to ATA*/ + /* This works around possible data corruption. + + On certain SATA controllers that can be seen when the r/w + command is given to the controller before the host DMA is + started. + + On a Read command, the controller would initiate the + command to the drive even before it sees the DMA + start. When there are very fast drives connected to the + controller, or when the data request hits in the drive + cache, there is the possibility that the drive returns a + part or all of the requested data to the controller before + the DMA start is issued. In this case, the controller + would become confused as to what to do with the data. In + the worst case when all the data is returned back to the + controller, the controller could hang. In other cases it + could return partial data returning in data + corruption. This problem has been seen in PPC systems and + can also appear on an system with very fast disks, where + the SATA controller is sitting behind a number of bridges, + and hence there is significant latency between the r/w + command and the start command. */ + /* issue r/w command if the access is to ATA */ if (qc->tf.protocol == ATA_PROT_DMA) ap->ops->sff_exec_command(ap, &qc->tf); }
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