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    SubjectRe: [PATCH v3] libata/ahci: Drop PCS quirk for Denverton and beyond
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    On 8/29/19 5:30 PM, Dan Williams wrote:
    > The Linux ahci driver has historically implemented a configuration fixup
    > for platforms / platform-firmware that fails to enable the ports prior
    > to OS hand-off at boot. The fixup was originally implemented way back
    > before ahci moved from drivers/scsi/ to drivers/ata/, and was updated in
    > 2007 via commit 49f290903935 "ahci: update PCS programming". The quirk
    > sets a port-enable bitmap in the PCS register at offset 0x92.
    >
    > This quirk could be applied generically up until the arrival of the
    > Denverton (DNV) platform. The DNV AHCI controller architecture supports
    > more than 6 ports and along with that the PCS register location and
    > format were updated to allow for more possible ports in the bitmap. DNV
    > AHCI expands the register to 32-bits and moves it to offset 0x94.
    >
    > As it stands there are no known problem reports with existing Linux
    > trying to set bits at offset 0x92 which indicates that the quirk is not
    > applicable. Likely it is not applicable on a wider range of platforms,
    > but it is difficult to discern which platforms if any still depend on
    > the quirk.
    >
    > Rather than try to fix the PCS quirk to consider the DNV register layout
    > instead require explicit opt-in. The assumption is that the OS driver
    > need not touch this register, and platforms can be added with a new
    > boad_ahci_pcs7 board-id when / if problematic platforms are found in the
    > future. The logic in ahci_intel_pcs_quirk() looks for all Intel AHCI
    > instances with "legacy" board-ids and otherwise skips the quirk if the
    > board was matched by class-code.

    Applied, thanks Dan.

    --
    Jens Axboe

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