Re: [PATCH v6 5/6] fbdev: Move framebuffer I/O helpers into <asm/fb.h>

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Thomas Zimmermann <tzimmermann@suse.de>,
	kernel test robot <lkp@intel.com>, Helge Deller <deller@gmx.de>,
	Javier Martinez Canillas <javierm@redhat.com>,
	Daniel Vetter <daniel@ffwll.ch>, Vineet Gupta <vgupta@kernel.org>,
	Huacai Chen <chenhuacai@kernel.org>,
	WANG Xuerui <kernel@xen0n.name>,
	"David S . Miller" <davem@davemloft.net>,
	"James E . J . Bottomley" <James.Bottomley@hansenpartnership.com>,
	Sam Ravnborg <sam@ravnborg.org>,
	suijingfeng@loongson.cn, oe-kbuild-all@lists.linux.dev,
	Linux-Arch <linux-arch@vger.kernel.org>,
	linux-fbdev@vger.kernel.org, linux-ia64@vger.kernel.org,
	linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linux-m68k@lists.linux-m68k.org,
	loongarch@lists.linux.dev, sparclinux@vger.kernel.org,
	linux-snps-arc@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	Artur Rojek <contact@artur-rojek.eu>
Subject: Re: [PATCH v6 5/6] fbdev: Move framebuffer I/O helpers into <asm/fb.h>
Date: Thu, 11 May 2023 14:35:51 +0200	[thread overview]
Message-ID: <CAMuHMdVvR1jdbZS8KoMf4R3zhLRWKv9XbG61iBGOGGZPHB+taA@mail.gmail.com> (raw)
In-Reply-To: <743d2b1e-c843-4fb2-b252-0006be2e2bd8@app.fastmail.com>

Hi Arnd,

CC Artur, who's working on HP Jornada 680.

On Wed, May 10, 2023 at 5:55 PM Arnd Bergmann <arnd@arndb.de> wrote:
> On Wed, May 10, 2023, at 16:27, Thomas Zimmermann wrote:
> > Am 10.05.23 um 16:15 schrieb Arnd Bergmann:
> >> On Wed, May 10, 2023, at 16:03, kernel test robot wrote:
>
> >> I think that's a preexisting bug and I have no idea what the
> >> correct solution is. Looking for HD64461 shows it being used
> >> both with inw/outw and readw/writew, so there is no way to have
> >> the correct type. The sh __raw_readw() definition hides this bug,
> >> but that is a problem with arch/sh and it probably hides others
> >> as well.
> >
> > The constant HD64461_IOBASE is defined as integer at
> >
> >
> > https://elixir.bootlin.com/linux/latest/source/arch/sh/include/asm/hd64461.h#L17
> >
> > but fb_readw() expects a volatile-void pointer. I guess we could add a
> > cast somewhere to silence the problem. In the current upstream code,
> > that appears to be done by sh's __raw_readw() internally:
> >
> >
> > https://elixir.bootlin.com/linux/latest/source/arch/sh/include/asm/io.h#L35
>
> Sure, that would make it build again, but that still doesn't make the
> code correct, since it's completely unclear what base address the
> HD64461_IOBASE is relative to. The hp6xx platform code only passes it
> through inw()/outw(), which take an offset relative to sh_io_port_base,
> but that is not initialized on hp6xx. I tried to find in the history
> when it broke, apparently that was in 2007 commit 34a780a0afeb ("sh:
> hp6xx pata_platform support."), which removed the custom inw/outw
> implementations.

See also commit 4aafae27d0ce73f8 ("sh: hd64461 tidying."), which
claims they are no longer needed.

Don't the I/O port macros just treat the port as an absolute base address
when sh_io_port_base isn't set?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds