[+cc Alan]
On Mon, Oct 09, 2017 at 11:56:43AM +0300, Adrian Hunter wrote:
> On 06/10/17 19:20, Bjorn Helgaas wrote:
> > On Fri, Oct 06, 2017 at 03:50:59PM +0300, Adrian Hunter wrote:
> >> The default D3 cold delay of 100 ms can cause pauses when streaming audio
> >> from eMMC.
> >>
> >> Intel BYT-related host controllers do not need PCI D3 delays. Although the
> >> delays can be set to zero via an ACPI _DSM, unfortunately that is not being
> >> used in all cases. So just set the delays to zero in the driver.
> >>
> >> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> >> ---
> >> drivers/mmc/host/sdhci-pci-core.c | 17 +++++++++++++----
> >> 1 file changed, 13 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/mmc/host/sdhci-pci-core.c b/drivers/mmc/host/sdhci-pci-core.c
> >> index 5f3f7b51299f..14ef99b6e5b7 100644
> >> --- a/drivers/mmc/host/sdhci-pci-core.c
> >> +++ b/drivers/mmc/host/sdhci-pci-core.c
> >> @@ -592,9 +592,18 @@ static void byt_read_dsm(struct sdhci_pci_slot *slot)
> >> slot->chip->rpm_retune = intel_host->d3_retune;
> >> }
> >>
> >> -static int byt_emmc_probe_slot(struct sdhci_pci_slot *slot)
> >> +static void byt_common_setup(struct sdhci_pci_slot *slot)
> >> {
> >> byt_read_dsm(slot);
> >> +
> >> + /* PCI D3 delays are not needed */
> >> + slot->chip->pdev->d3_delay = 0;
> >> + slot->chip->pdev->d3cold_delay = 0;
> >
> > The fact that it doesn't need D3 delays sounds like a property of the
> > device itself, regardless of which (if any) driver claims it.
> >
> > Can this be done as a quirk instead, maybe something in
> > arch/x86/pci/fixup.c? Maybe quirk_remove_d3_delay() could be used
> > directly, or something like pci_d3_delay_fixup()?
>
> A quirk would work, but that would mean setting the quirk for each device
> (28 so far) and then, when we have new ids, adding them there and to the
> driver, so it is more convenient just to do it in the driver. Certainly,
> this is the only driver we have for these Intel SDHCI PCI host controllers.
pci_d3_delay_fixup() has code that mitigates the problem of adding new
IDs. Maybe that quirk should simply be moved to arch/x86/pci/fixup.c?
If we put this in the driver, won't we have the unnecessary delays on
systems where the driver isn't in use?
Bjorn
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