Re: [PATCH v8 3/5] drm: handle HAS_IOPORT dependencies

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi

Am 21.10.24 um 12:08 schrieb Arnd Bergmann:
> On Mon, Oct 21, 2024, at 07:52, Thomas Zimmermann wrote:
> > Am 08.10.24 um 14:39 schrieb Niklas Schnelle:
> d 100644
> > > --- a/drivers/gpu/drm/qxl/Kconfig
> > > +++ b/drivers/gpu/drm/qxl/Kconfig
> > > @@ -2,6 +2,7 @@
> > >    config DRM_QXL
> > >    	tristate "QXL virtual GPU"
> > >    	depends on DRM && PCI && MMU
> > > +	depends on HAS_IOPORT
> > Is there a difference between this style (multiple 'depends on') and the
> > one used for gma500 (&& && &&)?
> No, it's the same. Doing it in one line is mainly useful
> if you have some '||' as well.
>
> > > @@ -105,7 +106,9 @@ static void bochs_vga_writeb(struct bochs_device *bochs, u16 ioport, u8 val)
> > >    
> > >    		writeb(val, bochs->mmio + offset);
> > >    	} else {
> > > +#ifdef CONFIG_HAS_IOPORT
> > >    		outb(val, ioport);
> > > +#endif
> > Could you provide empty defines for the out() interfaces at the top of
> > the file?
> That no longer works since there are now __compiletime_error()
> versions of these funcitons. However we can do it more nicely like:
>
> diff --git a/drivers/gpu/drm/tiny/bochs.c b/drivers/gpu/drm/tiny/bochs.c
> index 9b337f948434..034af6e32200 100644
> --- a/drivers/gpu/drm/tiny/bochs.c
> +++ b/drivers/gpu/drm/tiny/bochs.c
> @@ -112,14 +112,12 @@ static void bochs_vga_writeb(struct bochs_device *bochs, u16 ioport, u8 val)
>   	if (WARN_ON(ioport < 0x3c0 || ioport > 0x3df))
>   		return;
>   
> -	if (bochs->mmio) {
> +	if (!IS_DEFINED(CONFIG_HAS_IOPORT) || bochs->mmio) {
>   		int offset = ioport - 0x3c0 + 0x400;
>   
>   		writeb(val, bochs->mmio + offset);
>   	} else {
> -#ifdef CONFIG_HAS_IOPORT
>   		outb(val, ioport);
> -#endif
>   	}

For all functions with such a pattern, could we use:

bool bochs_uses_mmio(bochs)
{
    return !IS_DEFINED(CONFIG_HAS_IOPORT) || bochs->mmio
}

void writeb_func()
{
    if (bochs_uses_mmio()) {
      writeb()
#if CONFIG_HAS_IOPORT
    } else {
      outb()
#endif
    }
}

u8 readb_func()
{
    u8 ret = 0xff
    if (bochs_uses_mmio()) {
      ret = readb()
#if CONFIG_HAS_IOPORT
    } else {
      ret = inb()
#endif
    }
    return ret;
}

?

The code in bochs_uses_mmio() could then also print a drm_warn_once if 
we have neither MMIO nor I/O ports.

I'd review a separate series for such a change.

>   }
>   
> @@ -128,16 +126,12 @@ static u8 bochs_vga_readb(struct bochs_device *bochs, u16 ioport)
>   	if (WARN_ON(ioport < 0x3c0 || ioport > 0x3df))
>   		return 0xff;
>   
> -	if (bochs->mmio) {
> +	if (!IS_DEFINED(CONFIG_HAS_IOPORT) || bochs->mmio) {
>   		int offset = ioport - 0x3c0 + 0x400;
>   
>   		return readb(bochs->mmio + offset);
>   	} else {
> -#ifdef CONFIG_HAS_IOPORT
>   		return inb(ioport);
> -#else
> -		return 0xff;
> -#endif
>   	}
>   }
>   
> @@ -145,32 +139,26 @@ static u16 bochs_dispi_read(struct bochs_device *bochs, u16 reg)
>   {
>   	u16 ret = 0;
>   
> -	if (bochs->mmio) {
> +	if (!IS_DEFINED(CONFIG_HAS_IOPORT) || bochs->mmio) {
>   		int offset = 0x500 + (reg << 1);
>   
>   		ret = readw(bochs->mmio + offset);
>   	} else {
> -#ifdef CONFIG_HAS_IOPORT
>   		outw(reg, VBE_DISPI_IOPORT_INDEX);
>   		ret = inw(VBE_DISPI_IOPORT_DATA);
> -#else
> -		ret = 0xffff;
> -#endif
>   	}
>   	return ret;
>   }
>   
>   static void bochs_dispi_write(struct bochs_device *bochs, u16 reg, u16 val)
>   {
> -	if (bochs->mmio) {
> +	if (!IS_DEFINED(CONFIG_HAS_IOPORT) || bochs->mmio) {
>   		int offset = 0x500 + (reg << 1);
>   
>   		writew(val, bochs->mmio + offset);
>   	} else {
> -#ifdef CONFIG_HAS_IOPORT
>   		outw(reg, VBE_DISPI_IOPORT_INDEX);
>   		outw(val, VBE_DISPI_IOPORT_DATA);
> -#endif
>   	}
>   }
>   
> > And the in() interfaces could be defined to 0xff[ff].
> >
> > I assume that you don't want to provide such empty macros in the
> > kernel's io.h header?
> That was the original idea many years ago, but Linus rejected
> my pull request for it, so Niklas worked through all drivers
> individually to add the dependencies instead.

I see.

Best regards
Thomas

>       Arnd

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)