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Subject: Re: [PATCH v3] libata/ahci: Drop PCS quirk for Denverton and beyond
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     Stephen Douthit <stephend@silicom-usa.com>,
        Christoph Hellwig <hch@infradead.org>,
        linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org
References: <156712139395.1614755.3489977733530873708.stgit@dwillia2-desk3.amr.corp.intel.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <73e48d44-631a-71f9-4437-292c5b480891@kernel.dk>
Date:   Fri, 30 Aug 2019 20:54:04 -0600
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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