Re: [PATCH v2 2/2] asm-generic: Add new pci.h and use it

From: Arnd Bergmann <arnd@arndb.de>
To: Christoph Hellwig <hch@infradead.org>
Cc: Stafford Horne <shorne@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Guo Ren <guoren@kernel.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Richard Weinberger <richard@nod.at>,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>,
	Johannes Berg <johannes@sipsolutions.net>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	linux-csky@vger.kernel.org,
	linux-riscv <linux-riscv@lists.infradead.org>,
	linux-um <linux-um@lists.infradead.org>,
	linux-pci <linux-pci@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] asm-generic: Add new pci.h and use it
Date: Mon, 18 Jul 2022 08:56:20 +0200	[thread overview]
Message-ID: <CAK8P3a1KJe4K5g1z-Faoxc9NhXqjCUWxnvk2HPxsj2wzG_iDbg@mail.gmail.com> (raw)
In-Reply-To: <YtTjeEnKr8f8z4JS@infradead.org>

On Mon, Jul 18, 2022 at 6:37 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Sun, Jul 17, 2022 at 12:34:53PM +0900, Stafford Horne wrote:
> > Two things to note are:
> >
> >  - isa_dma_bridge_buggy, traditionally this is defined in asm/dma.h but
> >    these architectures avoid creating that file and add the definition
> >    to asm/pci.h.
>
> This doesn't have anyting to do with PCI support.  I think adding a
> separate header just for this that always stubs it out unless a config
> option is set (which x86 then selects) is the besy idea here.  I also
> think the isa_dma_bridge_buggy needs to move out of the PCI code as
> well.

Most architectures have it in asm/dma.h, which is probably the right place
(if we end up keeping it), since this is for the ISA DMA API.

I would copy this declaration from x86

#ifdef CONFIG_PCI
extern int isa_dma_bridge_buggy;
#else
#define isa_dma_bridge_buggy (0)
#endif

to asm-generic/dma.h and remove it from arch/sh to avoid the
one duplicate definition. The architectures that have the declaration
in asm/pci.h (arm64, csky, riscv) already get the asm-generic version
of asm/dma.h.

As mentioned before, it would be even better to just remove it
entirely from everything except x86, and enclose the four
references in an explicit "#ifdef X86_32". The variable declaration
only exists because drivers/pci/quirks.c is compiled on all
architecture, but the individual quirk is only active  based on
the PCI device ID of certain early PCI-ISA bridges.

      Arnd