linux-kernel - Re: [PATCH v2] i915: Support Intel GPU porting on any non-x86 system.

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Message-ID: <bac7a05b799309fe2c269232e70e82f86a8e2811@intel.com>
Date: Mon, 24 Nov 2025 14:24:47 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: zhangzhijie <zhangzhijie@...c.ac.cn>, jeff@...fgeerling.com,
 zhangzhijie@...c.ac.cn, wangran@...c.ac.cn, zhangjian@...c.ac.cn,
 daniel@...ll.ch, rodrigo.vivi@...el.com, joonas.lahtinen@...ux.intel.com,
 tursulin@...ulin.net, airlied@...il.com, intel-gfx@...ts.freedesktop.org,
 intel-xe@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, guoyaxing@...c.ac.cn
Subject: Re: [PATCH v2] i915: Support Intel GPU porting on any non-x86 system.

On Mon, 24 Nov 2025, zhangzhijie <zhangzhijie@...c.ac.cn> wrote:
> inb/outb speccial wire not support on other ARCH.
> Should detect whether arch platform support or not.

Seems to me it inb/outb depend on CONFIG_HAS_IOPORT. Which arch are you
talking about specifically?

> Signed-off-by: zhangzhijie <zhangzhijie@...c.ac.cn>
> ---
>  drivers/gpu/drm/i915/display/intel_vga.c | 27 ++++++++++++++++++------
>  1 file changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_vga.c b/drivers/gpu/drm/i915/display/intel_vga.c
> index 6e125564db34..d5d6c4ba6434 100644
> --- a/drivers/gpu/drm/i915/display/intel_vga.c
> +++ b/drivers/gpu/drm/i915/display/intel_vga.c
> @@ -41,6 +41,15 @@ static bool has_vga_pipe_sel(struct intel_display *display)
>  	return DISPLAY_VER(display) < 7;
>  }
>  
> +static bool intel_arch_support_vga_pm(struct intel_display *display)
> +{
> +#if defined(CONFIG_X86) || defined(CONFIG_X86_64)
> +	return true;
> +#else
> +	return false;
> +#endif
> +}
> +
>  /* Disable the VGA plane that we never use */
>  void intel_vga_disable(struct intel_display *display)
>  {
> @@ -66,11 +75,13 @@ void intel_vga_disable(struct intel_display *display)
>  
>  	/* WaEnableVGAAccessThroughIOPort:ctg,elk,ilk,snb,ivb,vlv,hsw */
>  	vga_get_uninterruptible(pdev, VGA_RSRC_LEGACY_IO);
> -	outb(0x01, VGA_SEQ_I);
> -	sr1 = inb(VGA_SEQ_D);
> -	outb(sr1 | VGA_SR01_SCREEN_OFF, VGA_SEQ_D);
> -	vga_put(pdev, VGA_RSRC_LEGACY_IO);
> -	udelay(300);
> +	if (likely(intel_arch_support_vga_pm(display))) {

As a rule of thumb, please do not use likely/unlikely, at all.

Here, intel_arch_support_vga_pm() is evaluated at build time, and the
likely has no functional value, only dubious documentation value.

> +		outb(0x01, VGA_SEQ_I);
> +		sr1 = inb(VGA_SEQ_D);
> +		outb(sr1 | VGA_SR01_SCREEN_OFF, VGA_SEQ_D);
> +		vga_put(pdev, VGA_RSRC_LEGACY_IO);

Both or neither get/put need to be inside the branch. Now you only get,
never put, on non-x86.

BR,
Jani.

> +		udelay(300);
> +	}
>  
>  	intel_de_write(display, vga_reg, VGA_DISP_DISABLE);
>  	intel_de_posting_read(display, vga_reg);
> @@ -91,8 +102,10 @@ void intel_vga_reset_io_mem(struct intel_display *display)
>  	 * and error messages.
>  	 */
>  	vga_get_uninterruptible(pdev, VGA_RSRC_LEGACY_IO);
> -	outb(inb(VGA_MIS_R), VGA_MIS_W);
> -	vga_put(pdev, VGA_RSRC_LEGACY_IO);
> +	if (likely(intel_arch_support_vga_pm(display))) {
> +		outb(inb(VGA_MIS_R), VGA_MIS_W);
> +		vga_put(pdev, VGA_RSRC_LEGACY_IO);
> +	}
>  }
>  
>  int intel_vga_register(struct intel_display *display)

-- 
Jani Nikula, Intel