linux-kernel - Re: [PATCH 0/1] scsi: qla1280: Make 64-bit DMA addressing a Kconfig option

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Message-ID: <CA+=Fv5QmqAFLyToOsCKzgWSdnMXGr7FjeW_fO5reTUgJJP27Sg@mail.gmail.com>
Date: Mon, 1 Sep 2025 23:41:41 +0200
From: Magnus Lindholm <linmag7@...il.com>
To: "Maciej W. Rozycki" <macro@...am.me.uk>
Cc: linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org, 
	linux-alpha@...r.kernel.org, martin.petersen@...cle.com, 
	James.Bottomley@...senpartnership.com, hch@...radead.org
Subject: Re: [PATCH 0/1] scsi: qla1280: Make 64-bit DMA addressing a Kconfig option

Hi,

> >  If it turns out a generic issue with DAC handling in the Tsunami chipset,
> > then a better approach would be a generic workaround for all potentially
> > affected devices, but it does not appear we have existing infrastructure
> > for that.  Just setting the global DMA mask would unnecessarily cripple
> > 64-bit option cards as well, but it seems to me there might be something
> > relevant in arch/mips/pci/fixup-sb1250.c; see `quirk_sb1250_pci_dac' and
> > the comments above it.

I've been taking a closer look at the quirk_sb1250_pci_dac. It should indeed
be possible to implement a similar workaround on Alpha. I believe that would
require some fixes to the Alpha specific implementations in pci_iommu.c. For
one thing, the implementation does not respect 'dev->bus_dma_limit' which
is used in  the quirk_sb1250_pci_dac implementation.

I've put together a patch, and I'm testing it right now, that implements a quirk
similar to quirk_sb1250_pci_dac as well as makes stuff in pci_iommu.c take
'dev->bus_dma_limit' into consideration on Alpha. If this approach makes
sense I'll put out a new patch for review. Since this approach does not
touch the qla1280 SCSI driver, I won't send it to the linux-scsi list.

Regards

Magnus