From 6f5050a96c9e0521f42a3a1d676c7ad9815f62ad Mon Sep 17 00:00:00 2001 From: Bartlomiej Zolnierkiewicz Date: Sat, 17 Mar 2007 21:57:39 +0100 Subject: ide: don't allow DMA to be enabled if CONFIG_IDEDMA_{ICS,PCI}_AUTO=n For CONFIG_IDEDMA_{ICS,PCI}_AUTO=n and/or "ide=nodma" option the host/device are not programmed for DMA and it is also explicitly disabled by ide_set_dma() (->ide_dma_check returns "-1"). However the code responsible for manually enabling DMA ("hdparm -d 1") has a bug which results in DMA being erroneously enabled - ide_set_dma() incorrectly passes "0" return value to set_using_dma(). This may work if BIOS/firmware configured the host/device for DMA and chipset allows independent configuration of DMA/PIO modes but won't work after suspend and is generally unsafe on many chipsets (possibly including data corruption if the same registers are used for DMA/PIO timings). This patch fixes kernel bugzilla bug #8169 (piix host driver fixes for setting PIO mode exposed the problem described above). The side-effect of the fix is that some rare configuration may be forced to PIO mode when DMA mode was previously used - this is addressed by the next patch which removes CONFIG_IDEDMA_{PCI,ICS}_AUTO config option completely. Thanks goes out to Patrick Horn for reporting the issue, narrowing it down to the specific commit and testing the fix. Also thanks to Sergei Shtylyov for help in debugging the problem. Cc: Patrick Horn Cc: Sergei Shtylyov Cc: Russell King Signed-off-by: Bartlomiej Zolnierkiewicz --- drivers/ide/ide-dma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers') diff --git a/drivers/ide/ide-dma.c b/drivers/ide/ide-dma.c index 08e7cd043bc..fd213088b06 100644 --- a/drivers/ide/ide-dma.c +++ b/drivers/ide/ide-dma.c @@ -767,7 +767,7 @@ int ide_set_dma(ide_drive_t *drive) switch(rc) { case -1: /* DMA needs to be disabled */ hwif->dma_off_quietly(drive); - return 0; + return -1; case 0: /* DMA needs to be enabled */ return hwif->ide_dma_on(drive); case 1: /* DMA setting cannot be changed */ -- cgit v1.2.3-70-g09d2