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    SubjectRe: [RFC][PATCH] 2.4 IDE Serverworks OSB4 DMA patch
    Date
    On Thursday 29 of April 2004 21:04, Patrick Wildi wrote:
    > I have been using a OSB4 chipset based system with a CompactFlash
    > that supports PIO only and a laptop IBM/Hitachi Travelstar HDD
    > that supports UDMA.
    > For both drives, the serverworks code misconfigures the drives:
    >
    > - for the CF (hooked up as /dev/hda), svwks_config_drive_xfer_rate()
    > will not match any tests (drive->autodma = 0, id->capability = 2,
    > id->field_valid = 1), but the function will then call
    > hwif->ide_dma_on(drive), which it should not do for this drive.
    > This patch moves the enabling of DMA up into the DMA section of
    > the code.

    Yep, known bug, it is fixed in 2.6.

    It is present in many other drivers, my 2.6 patch needs to be backported.

    > - for the Travelstart HDD, the settings coming into
    > svwks_config_drive_xfer_rate() are: drive->autodma = 32,
    > id->capability = 15, id->field_valid = 7, id->dma_ultra = 0x43f.
    > But as this is an OSB4, the hwif->ultra_mask is set to not support
    > UDMA. Unfortunately in that case svwks_config_drive_xfer_rate()
    > falls through to the end of the function, instead of trying
    > other DMA modes.

    Good catch.

    It seems the same bug can be present in other drivers too (hint, hint). ;)

    > By adding a jump to try_dma_modes in the case that the drive
    > is UDMA capable but the mask does not allow UDMA, the drive
    > will be setup up for MWDMA.
    >
    > The logic in svwks_config_drive_xfer_rate() could probably be
    > improved a bit, but I kept the changes to an absolute minium
    > to reduce the risk of breakage.

    OK, thanks.

    > The patch is against 2.4.24, but the file has not changed in
    > 2.4.25 and 2.4.26.
    >
    > Patrick
    >
    >
    > --- linux-2.4.24-nam/drivers/ide/pci/serverworks.c.orig Thu Apr 22 17:31:28
    > 2004 +++ linux-2.4.24-nam/drivers/ide/pci/serverworks.c Thu Apr 29 11:02:05
    > 2004 @@ -473,7 +473,9 @@
    > int dma = config_chipset_for_dma(drive);
    > if ((id->field_valid & 2) && !dma)
    > goto try_dma_modes;
    > - }
    > + } else
    > + /* UDMA disabled by mask, try other DMA modes */
    > + goto try_dma_modes;
    > } else if (id->field_valid & 2) {
    > try_dma_modes:
    > if ((id->dma_mword & hwif->mwdma_mask) ||
    > @@ -490,6 +492,7 @@
    > } else {
    > goto no_dma_set;
    > }
    > + return hwif->ide_dma_on(drive);
    > } else if ((id->capability & 8) || (id->field_valid & 2)) {
    > fast_ata_pio:
    > no_dma_set:
    > @@ -497,7 +500,7 @@
    > // hwif->tuneproc(drive, 5);
    > return hwif->ide_dma_off_quietly(drive);
    > }
    > - return hwif->ide_dma_on(drive);
    > + return 0;
    > }
    >
    > /* This can go soon */

    -
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