linux-kernel - Re: [PATCH v4 38/41] video: handle HAS

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Message-ID: <db6db5d49e236548c26fbaa2e16462463814d7ff.camel@linux.ibm.com>
Date:   Wed, 17 May 2023 14:41:20 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Helge Deller <deller@....de>
Cc:     linux-arch@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
        linux-fbdev@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>,
        "Rafael J. Wysocki" <rafael@...nel.org>, linux-pci@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>
Subject: Re: [PATCH v4 38/41] video: handle HAS_IOPORT dependencies

On Tue, 2023-05-16 at 19:21 +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 16.05.23 um 13:00 schrieb Niklas Schnelle:
> > In a future patch HAS_IOPORT=n will result in inb()/outb() and friends
> > not being declared. We thus need to add HAS_IOPORT as dependency for
> > those drivers using them and guard inline code in headers.
> > 
> > Co-developed-by: Arnd Bergmann <arnd@...nel.org>
> > Signed-off-by: Arnd Bergmann <arnd@...nel.org>
> > Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> > ---
> > Note: The HAS_IOPORT Kconfig option was added in v6.4-rc1 so
> >        per-subsystem patches may be applied independently
> > 
> >   drivers/video/console/Kconfig |  1 +
> >   drivers/video/fbdev/Kconfig   | 21 +++++++++++----------
> >   include/video/vga.h           |  8 ++++++++
> 
> Those are 3 different things. It might be preferable to not handle them 
> under the video/ umbrella.
> 
> >   3 files changed, 20 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
> > index 22cea5082ac4..64974eaa3ac5 100644
> > --- a/drivers/video/console/Kconfig
> > +++ b/drivers/video/console/Kconfig
> > @@ -10,6 +10,7 @@ config VGA_CONSOLE
> >   	depends on !4xx && !PPC_8xx && !SPARC && !M68K && !PARISC &&  !SUPERH && \
> >   		(!ARM || ARCH_FOOTBRIDGE || ARCH_INTEGRATOR || ARCH_NETWINDER) && \
> >   		!ARM64 && !ARC && !MICROBLAZE && !OPENRISC && !S390 && !UML
> > +	depends on HAS_IOPORT
> >   	select APERTURE_HELPERS if (DRM || FB || VFIO_PCI_CORE)
> >   	default y
> >   	help
> > diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
> > index 96e91570cdd3..a56c57dd839b 100644
> > --- a/drivers/video/fbdev/Kconfig
> > +++ b/drivers/video/fbdev/Kconfig
> > @@ -335,7 +335,7 @@ config FB_IMX
> >   
> >   config FB_CYBER2000
> >   	tristate "CyberPro 2000/2010/5000 support"
> > -	depends on FB && PCI && (BROKEN || !SPARC64)
> > +	depends on FB && PCI && HAS_IOPORT && (BROKEN || !SPARC64)
> >   	select FB_CFB_FILLRECT
> >   	select FB_CFB_COPYAREA
> >   	select FB_CFB_IMAGEBLIT
> > @@ -429,6 +429,7 @@ config FB_FM2
> >   config FB_ARC
> >   	tristate "Arc Monochrome LCD board support"
> >   	depends on FB && (X86 || COMPILE_TEST)
> > +	depends on HAS_IOPORT
> >   	select FB_SYS_FILLRECT
> >   	select FB_SYS_COPYAREA
> >   	select FB_SYS_IMAGEBLIT
> > @@ -1332,7 +1333,7 @@ config FB_ATY_BACKLIGHT
> >   
> >   config FB_S3
> >   	tristate "S3 Trio/Virge support"
> > -	depends on FB && PCI
> > +	depends on FB && PCI && HAS_IOPORT
> >   	select FB_CFB_FILLRECT
> >   	select FB_CFB_COPYAREA
> >   	select FB_CFB_IMAGEBLIT
> > @@ -1393,7 +1394,7 @@ config FB_SAVAGE_ACCEL
> >   
> >   config FB_SIS
> >   	tristate "SiS/XGI display support"
> > -	depends on FB && PCI
> > +	depends on FB && PCI && HAS_IOPORT
> >   	select FB_CFB_FILLRECT
> >   	select FB_CFB_COPYAREA
> >   	select FB_CFB_IMAGEBLIT
> > @@ -1424,7 +1425,7 @@ config FB_SIS_315
> >   
> >   config FB_VIA
> >   	tristate "VIA UniChrome (Pro) and Chrome9 display support"
> > -	depends on FB && PCI && GPIOLIB && I2C && (X86 || COMPILE_TEST)
> > +	depends on FB && PCI && GPIOLIB && I2C && HAS_IOPORT && (X86 || COMPILE_TEST)
> >   	select FB_CFB_FILLRECT
> >   	select FB_CFB_COPYAREA
> >   	select FB_CFB_IMAGEBLIT
> > @@ -1463,7 +1464,7 @@ endif
> >   
> >   config FB_NEOMAGIC
> >   	tristate "NeoMagic display support"
> > -	depends on FB && PCI
> > +	depends on FB && PCI && HAS_IOPORT
> >   	select FB_MODE_HELPERS
> >   	select FB_CFB_FILLRECT
> >   	select FB_CFB_COPYAREA
> > @@ -1493,7 +1494,7 @@ config FB_KYRO
> >   
> >   config FB_3DFX
> >   	tristate "3Dfx Banshee/Voodoo3/Voodoo5 display support"
> > -	depends on FB && PCI
> > +	depends on FB && PCI && HAS_IOPORT
> >   	select FB_CFB_IMAGEBLIT
> >   	select FB_CFB_FILLRECT
> >   	select FB_CFB_COPYAREA
> > @@ -1543,7 +1544,7 @@ config FB_VOODOO1
> >   
> >   config FB_VT8623
> >   	tristate "VIA VT8623 support"
> > -	depends on FB && PCI
> > +	depends on FB && PCI && HAS_IOPORT
> >   	select FB_CFB_FILLRECT
> >   	select FB_CFB_COPYAREA
> >   	select FB_CFB_IMAGEBLIT
> > @@ -1558,7 +1559,7 @@ config FB_VT8623
> >   
> >   config FB_TRIDENT
> >   	tristate "Trident/CyberXXX/CyberBlade support"
> > -	depends on FB && PCI
> > +	depends on FB && PCI && HAS_IOPORT
> >   	select FB_CFB_FILLRECT
> >   	select FB_CFB_COPYAREA
> >   	select FB_CFB_IMAGEBLIT
> > @@ -1581,7 +1582,7 @@ config FB_TRIDENT
> >   
> >   config FB_ARK
> >   	tristate "ARK 2000PV support"
> > -	depends on FB && PCI
> > +	depends on FB && PCI && HAS_IOPORT
> >   	select FB_CFB_FILLRECT
> >   	select FB_CFB_COPYAREA
> >   	select FB_CFB_IMAGEBLIT
> > @@ -2195,7 +2196,7 @@ config FB_SSD1307
> >   
> >   config FB_SM712
> >   	tristate "Silicon Motion SM712 framebuffer support"
> > -	depends on FB && PCI
> > +	depends on FB && PCI && HAS_IOPORT
> >   	select FB_CFB_FILLRECT
> >   	select FB_CFB_COPYAREA
> >   	select FB_CFB_IMAGEBLIT
> > diff --git a/include/video/vga.h b/include/video/vga.h
> > index 947c0abd04ef..f4b806b85c86 100644
> > --- a/include/video/vga.h
> > +++ b/include/video/vga.h
> > @@ -203,18 +203,26 @@ extern int restore_vga(struct vgastate *state);
> >   
> >   static inline unsigned char vga_io_r (unsigned short port)
> >   {
> > +#ifdef CONFIG_HAS_IOPORT
> >   	return inb_p(port);
> > +#else
> > +	return 0xff;
> > +#endif
> >   }
> >   
> >   static inline void vga_io_w (unsigned short port, unsigned char val)
> >   {
> > +#ifdef CONFIG_HAS_IOPORT
> >   	outb_p(val, port);
> > +#endif
> >   }
> >   
> >   static inline void vga_io_w_fast (unsigned short port, unsigned char reg,
> >   				  unsigned char val)
> >   {
> > +#ifdef CONFIG_HAS_IOPORT
> >   	outw(VGA_OUT16VAL (val, reg), port);
> > +#endif
> >   }
> 
> It feels wrong that these helpers silently do nothing. I'd enclose them 
> in CONFIG_HAS_IOPORT entirely. The drivers that use them unconditionally 
> would then fail to build.
> 
> Best regards
> Thomas

Ok yeah, I was looking at the call sites like vga_w_fast() that use
either an HAS_IOPORT dependent function or a writew() based one and so
if I #ifdef the regbase != NULL check we could end up with a NULL
derference but I guess that is kind of what we want since clearly
something is wrong if the driver tries to do I/O port access despite it
not being available.

Thanks,
Niklas