Received-SPF: pass (google.com: domain of linux-kernel+bounces-94150-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Feedback-ID: i56a14606:Fastmail
User-Agent: Cyrus-JMAP/3.11.0-alpha0-208-g3f1d79aedb-fm-20240301.002-g3f1d79ae
Precedence: bulk
MIME-Version: 1.0
Message-Id: <9f6c9e65-d7f5-46cf-bdf8-9ff01b135ea9@app.fastmail.com>
In-Reply-To: <ZeiGBuMN_I9V94Mx@infradead.org>
References: 
 <20240224-sam-fix-sparc32-all-builds-v2-0-1f186603c5c4@ravnborg.org>
 <20240224-sam-fix-sparc32-all-builds-v2-4-1f186603c5c4@ravnborg.org>
 <8d5780f5-1047-48d7-a9c9-09b95c7b5604@gaisler.com>
 <5648dca0-4853-4dfb-91cf-282a656beb1e@app.fastmail.com>
 <bc33b608-e0b5-4dff-aa05-8513dce409b3@gaisler.com>
 <ZeiGBuMN_I9V94Mx@infradead.org>
Date: Wed, 06 Mar 2024 16:24:10 +0100
From: "Arnd Bergmann" <arnd@arndb.de>
To: "Christoph Hellwig" <hch@infradead.org>,
 "Andreas Larsson" <andreas@gaisler.com>
Cc: "Sam Ravnborg" <sam@ravnborg.org>,
 "Maciej W. Rozycki" <macro@orcam.me.uk>, sparclinux@vger.kernel.org,
 "Randy Dunlap" <rdunlap@infradead.org>,
 "Miquel Raynal" <miquel.raynal@bootlin.com>,
 linux-parport@lists.infradead.org, "David S . Miller" <davem@davemloft.net>,
 linux-kernel@vger.kernel.org, "Takashi Iwai" <tiwai@suse.de>,
 iommu@lists.linux.dev, linux-kbuild@vger.kernel.org,
 "Masahiro Yamada" <masahiroy@kernel.org>
Subject: Re: [PATCH v2 4/7] sparc32: Do not select ZONE_DMA
Content-Type: text/plain

On Wed, Mar 6, 2024, at 16:04, Christoph Hellwig wrote:
> 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.

It looks like it did not remain that way for long, as
2db1a57986d3 ("ALSA: pci: depend on ZONE_DMA") removed
the broken select again.

> 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).

It's a nice idea, but it would require a lot of reworks to get right,
with things like drivers/platform/x86 or drivers/{parisc,s390,sh}
that are still somewhat architecture code, and subsystems like
drivers/gpu/drm that typically just select whatever they want
instead of using dependencies.

      Arnd