linux-kernel - Re: [PATCH] drm/hyperv: Don't rely on screen_info.lfb

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Message-ID: <14302178-c797-8635-4325-070f78b7f805@suse.de>
Date:   Sat, 10 Sep 2022 20:11:24 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Saurabh Sengar <ssengar@...ux.microsoft.com>,
        ssengar@...rosoft.com, drawat.floss@...il.com, airlied@...ux.ie,
        daniel@...ll.ch, linux-hyperv@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        mikelley@...rosoft.com
Subject: Re: [PATCH] drm/hyperv: Don't rely on screen_info.lfb_base for Gen1
 VMs

Hi

Am 09.09.22 um 16:43 schrieb Saurabh Sengar:
> hyperv_setup_vram tries to remove conflicting framebuffer based on
> 'screen_info'. As observed in past due to some bug or wrong setting
> in grub, the 'screen_info' fields may not be set for Gen1, and in such
> cases drm_aperture_remove_conflicting_framebuffers will not do anything
> useful.
> For Gen1 VMs, it should always be possible to get framebuffer
> conflict removed using PCI device instead.
> 
> Fixes: a0ab5abced55 ("drm/hyperv : Removing the restruction of VRAM allocation with PCI bar size")
> Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> ---
>   drivers/gpu/drm/hyperv/hyperv_drm_drv.c | 24 ++++++++++++++++++++----
>   1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_drv.c b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
> index 6d11e7938c83..b0cc974efa45 100644
> --- a/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
> +++ b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
> @@ -73,12 +73,28 @@ static int hyperv_setup_vram(struct hyperv_drm_device *hv,
>   			     struct hv_device *hdev)
>   {
>   	struct drm_device *dev = &hv->dev;
> +	struct pci_dev *pdev;
>   	int ret;
>   
> -	drm_aperture_remove_conflicting_framebuffers(screen_info.lfb_base,
> -						     screen_info.lfb_size,
> -						     false,
> -						     &hyperv_driver);
> +	if (efi_enabled(EFI_BOOT)) {
> +		drm_aperture_remove_conflicting_framebuffers(screen_info.lfb_base,
> +							     screen_info.lfb_size,

Using screen_info here seems wrong in any case. You want to remove the 
framebuffer devices that conflict with your driver, which might be 
unrelated to screen_info. AFAICT the correct solution would always 
retrieve the PCI device for removal (i.e., always do the else branch).

Best regard
Thomas

> +							     false,
> +							     &hyperv_driver);
> +	} else {
> +		pdev = pci_get_device(PCI_VENDOR_ID_MICROSOFT, PCI_DEVICE_ID_HYPERV_VIDEO, NULL);
> +		if (!pdev) {
> +			drm_err(dev, "Unable to find PCI Hyper-V video\n");
> +			return -ENODEV;
> +		}
> +
> +		ret = drm_aperture_remove_conflicting_pci_framebuffers(pdev, &hyperv_driver);
> +		pci_dev_put(pdev);
> +		if (ret) {
> +			drm_err(dev, "Not able to remove boot fb\n");
> +			return ret;
> +		}
> +	}
>   
>   	hv->fb_size = (unsigned long)hv->mmio_megabytes * 1024 * 1024;
>   

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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