linux-kernel - Re: [PATCH] xen/x86: obtain upper 32 bits of video frame buffer address for Dom0

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Date:   Tue, 4 Jan 2022 11:50:21 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Jan Beulich <jbeulich@...e.com>, Juergen Gross <jgross@...e.com>
Cc:     "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen/x86: obtain upper 32 bits of video frame buffer
 address for Dom0


On 1/4/22 3:46 AM, Jan Beulich wrote:
> The hypervisor has been supplying this information for a couple of major
> releases. Make use of it. The need to set a flag in the capabilities
> field also points out that the prior setting of that field from the
> hypervisor interface's gbl_caps one was wrong, so that code gets deleted
> (there's also no equivalent of this in native boot code).
>
> Signed-off-by: Jan Beulich <jbeulich@...e.com>
>
> --- a/arch/x86/xen/vga.c
> +++ b/arch/x86/xen/vga.c
> @@ -63,13 +63,17 @@ void __init xen_init_vga(const struct do
>   		}
>   
>   		if (size >= offsetof(struct dom0_vga_console_info,
> -				     u.vesa_lfb.gbl_caps)
> -		    + sizeof(info->u.vesa_lfb.gbl_caps))
> -			screen_info->capabilities = info->u.vesa_lfb.gbl_caps;
> -		if (size >= offsetof(struct dom0_vga_console_info,
>   				     u.vesa_lfb.mode_attrs)
>   		    + sizeof(info->u.vesa_lfb.mode_attrs))


Do we still need this test? All 4.0+ hypervisors will have mode_attrs.


-boris



>   			screen_info->vesa_attributes = info->u.vesa_lfb.mode_attrs;
> +
> +		if (size >= offsetof(struct dom0_vga_console_info,
> +				     u.vesa_lfb.ext_lfb_base)
> +		    + sizeof(info->u.vesa_lfb.ext_lfb_base)
> +		    && info->u.vesa_lfb.ext_lfb_base) {
> +			screen_info->ext_lfb_base = info->u.vesa_lfb.ext_lfb_base;
> +			screen_info->capabilities |= VIDEO_CAPABILITY_64BIT_BASE;
> +		}
>   		break;
>   	}
>   }
> --- a/include/xen/interface/xen.h
> +++ b/include/xen/interface/xen.h
> @@ -722,6 +722,9 @@ struct dom0_vga_console_info {
>   			uint32_t gbl_caps;
>   			/* Mode attributes (offset 0x0, VESA command 0x4f01). */
>   			uint16_t mode_attrs;
> +			uint16_t pad;
> +			/* high 32 bits of lfb_base */
> +			uint32_t ext_lfb_base;
>   		} vesa_lfb;
>   	} u;
>   };
>