linux-kernel - Re: [PATCH v2 4/7] sparc32: Do not select ZONE

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Date: Wed, 6 Mar 2024 07:04:38 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Andreas Larsson <andreas@...sler.com>
Cc: Arnd Bergmann <arnd@...db.de>, Sam Ravnborg <sam@...nborg.org>,
	"Maciej W. Rozycki" <macro@...am.me.uk>, sparclinux@...r.kernel.org,
	Randy Dunlap <rdunlap@...radead.org>,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	linux-parport@...ts.infradead.org,
	"David S . Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, Takashi Iwai <tiwai@...e.de>,
	iommu@...ts.linux.dev, linux-kbuild@...r.kernel.org,
	Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH v2 4/7] sparc32: Do not select ZONE_DMA

On Wed, Mar 06, 2024 at 03:19:52PM +0100, Andreas Larsson wrote:
> > I think that is the correct thing to do then: the only
> > drivers that I see with this dependency are PCI sound cards
> > that apparently rely on DMA to the 16MB ISA range, which is
> > not provided by sparc.
> 
> The ZONE_DMA dependency does not seem related to ISA per se. Commit
> 80ab8eae70e5 ("ALSA: Enable CONFIG_ZONE_DMA for smaller PCI DMA masks")
> that started to introduce it did were about ensuring 32-bit masks.

Yikes!  That commit is just unbelievable buggy.  CONFIG_ZONE_DMA
is only for architetures to select, not drivers.  A driver randomly
enabling such an arch zone is just crazy.

I've been wondering for a while if we need some Kconfig magic
so that certain symbols can only be select from arch/* and not
elsewhere to prevent this (we had a few other similar cases like
DMA_MAP_OPS).