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pnp: restore automatic resolution of DMA conflicts

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To fix a 5-year-old regression, reverse changes made by commit
7ef3639 (PNP: don't fail device init if no DMA channel available).

As an example to show the problem, my sound card provides a
prioritized list of PnP "dependent sets" of requested resources:

  dependent set 0 (preferred) wants DMA 5.
  dependent set 1 (acceptable) will take DMA 5, 6, or 7.
  ...
  dependent set 4 (acceptable) doesn't request a high DMA.

If DMA 5 is not available, pnp_assign_dma has to fail on set 0 so that
pnp_auto_config_dev will move on to set 1 and get DMA 6 or 7.
Instead, pnp_assign_dma adds the resource with flags |=
IORESOURCE_DISABLED and returns success.  pnp_auto_config_dev just
sees success and therefore chooses set 0 with a disabled DMA and never
tries the sets that would have resolved the conflict.

Furthermore, this mode of "success" is unexpected and unhandled in
sound/isa/sb and probably other drivers.  sb assumes that the returned
DMA is enabled and obliviously uses the invalid DMA number.  Observed
consequences were sb successfully grabbing a DMA that was expressly
forbidden by the kernel parameter pnp_reserve_dma.

The only upside to the original change would be as a kludge for
devices that can operate in degraded mode without a DMA but that don't
provide the corresponding non-preferred dependent set.  The right
workaround for those devices is to synthesize the missing set in
quirks.c; otherwise, you're reinventing PnP fallback functionality at
the driver level for that device and all others.

Signed-off-by: David Flater <dave@flaterco.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
David Flater 2013-05-10 14:37:43 +02:00 committed by Rafael J. Wysocki
parent c7788792a5
commit bdf0eb3a02
1 changed files with 9 additions and 5 deletions
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14
drivers/pnp/manager.c
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@ -211,6 +211,12 @@ static int pnp_assign_dma(struct pnp_dev *dev, struct pnp_dma *rule, int idx)
res->start = -1;
res->end = -1;
if (!rule->map) {
res->flags |= IORESOURCE_DISABLED;
pnp_dbg(&dev->dev, " dma %d disabled\n", idx);
goto __add;
}
for (i = 0; i < 8; i++) {
if (rule->map & (1 << xtab[i])) {
res->start = res->end = xtab[i];
@ -218,11 +224,9 @@ static int pnp_assign_dma(struct pnp_dev *dev, struct pnp_dma *rule, int idx)
goto __add;
}
}
#ifdef MAX_DMA_CHANNELS
res->start = res->end = MAX_DMA_CHANNELS;
#endif
res->flags |= IORESOURCE_DISABLED;
pnp_dbg(&dev->dev, " disable dma %d\n", idx);
pnp_dbg(&dev->dev, " couldn't assign dma %d\n", idx);
return -EBUSY;
__add:
pnp_add_dma_resource(dev, res->start, res->flags);