[PATCH] drm/hyperv: Don't rely on screen_info.lfb_base for Gen1 VMs

[PATCH] drm/hyperv: Don't rely on screen_info.lfb_base for Gen1 VMs

[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@linux.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,
+							     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;
 
-- 
2.34.1

RE: [PATCH] drm/hyperv: Don't rely on screen_info.lfb_base for Gen1 VMs

[Michael Kelley (LINUX)]

From: Saurabh Sengar <ssengar@linux.microsoft.com> Sent: Friday, September 9, 2022 7:44 AM
> 
> 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@linux.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,
> +							     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;
> 
> --
> 2.34.1

Reviewed-by: Michael Kelley <mikelley@microsoft.com>

Re: [PATCH] drm/hyperv: Don't rely on screen_info.lfb_base for Gen1 VMs

[Thomas Zimmermann]

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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@linux.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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Re: [PATCH] drm/hyperv: Don't rely on screen_info.lfb_base for Gen1 VMs

[Saurabh Singh Sengar]

On Sat, Sep 10, 2022 at 08:11:24PM +0200, Thomas Zimmermann wrote:
> 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@linux.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).

In a Gen2 VM, the Hyper-V frame buffer device is presented only as a VMbus device.
It's not presented as a PCI device like it is in a Gen1 VM. This would have worked
if we had the frame buffer device available as PCI device in Gen2 but unfortunately
thats not the case here.

Regards,
Saurabh

> 
> 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

Re: [PATCH] drm/hyperv: Don't rely on screen_info.lfb_base for Gen1 VMs

[Thomas Zimmermann]

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Hi

Am 11.09.22 um 18:21 schrieb Saurabh Singh Sengar:
> On Sat, Sep 10, 2022 at 08:11:24PM +0200, Thomas Zimmermann wrote:
>> 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@linux.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).
> 
> In a Gen2 VM, the Hyper-V frame buffer device is presented only as a VMbus device.
> It's not presented as a PCI device like it is in a Gen1 VM. This would have worked
> if we had the frame buffer device available as PCI device in Gen2 but unfortunately
> thats not the case here.

Thanks for explaining. There is an instance of struct hv_device passed 
to the probe function. I suspect you cannot get the framebuffer range 
from this instance (e.g., via the device's platform_data)?

If you absolutely can't get the actual memory region from the device, 
it's better to remove all framebuffers via 
drm_aperture_remove_framebuffers() than to use screen_info.

Best regards
Thomas

> 
> Regards,
> Saurabh
> 
>>
>> 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
> 
> 
> 

-- 
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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Re: [PATCH] drm/hyperv: Don't rely on screen_info.lfb_base for Gen1 VMs

[Saurabh Singh Sengar]

On Mon, Sep 12, 2022 at 09:03:53AM +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 11.09.22 um 18:21 schrieb Saurabh Singh Sengar:
> >On Sat, Sep 10, 2022 at 08:11:24PM +0200, Thomas Zimmermann wrote:
> >>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@linux.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).
> >
> >In a Gen2 VM, the Hyper-V frame buffer device is presented only as a VMbus device.
> >It's not presented as a PCI device like it is in a Gen1 VM. This would have worked
> >if we had the frame buffer device available as PCI device in Gen2 but unfortunately
> >thats not the case here.
> 
> Thanks for explaining. There is an instance of struct hv_device
> passed to the probe function. I suspect you cannot get the
> framebuffer range from this instance (e.g., via the device's
> platform_data)?
> 
> If you absolutely can't get the actual memory region from the
> device, it's better to remove all framebuffers via
> drm_aperture_remove_framebuffers() than to use screen_info.
> 
> Best regards
> Thomas

Thanks for your suggestion, and I thought of using drm_aperture_remove_framebuffers
here, but this driver will be used in many different systems with many other graphics
devices (GPU etc). Removing all the framebuffer is a bit blunt approach which may disturb
the devices we are not intended to and which are even outside of the HyperV MMIO region.
I feel this API use will be risky, and I would like to stick to the earlier method which
is proven to be working for many years and we are sure it won't disturb anyone outside
MMIO region.

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

Re: [PATCH] drm/hyperv: Don't rely on screen_info.lfb_base for Gen1 VMs

[Thomas Zimmermann]

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Hi

Am 13.09.22 um 17:15 schrieb Saurabh Singh Sengar:
> On Mon, Sep 12, 2022 at 09:03:53AM +0200, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 11.09.22 um 18:21 schrieb Saurabh Singh Sengar:
>>> On Sat, Sep 10, 2022 at 08:11:24PM +0200, Thomas Zimmermann wrote:
>>>> 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@linux.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).
>>>
>>> In a Gen2 VM, the Hyper-V frame buffer device is presented only as a VMbus device.
>>> It's not presented as a PCI device like it is in a Gen1 VM. This would have worked
>>> if we had the frame buffer device available as PCI device in Gen2 but unfortunately
>>> thats not the case here.
>>
>> Thanks for explaining. There is an instance of struct hv_device
>> passed to the probe function. I suspect you cannot get the
>> framebuffer range from this instance (e.g., via the device's
>> platform_data)?
>>
>> If you absolutely can't get the actual memory region from the
>> device, it's better to remove all framebuffers via
>> drm_aperture_remove_framebuffers() than to use screen_info.
>>
>> Best regards
>> Thomas
> 
> Thanks for your suggestion, and I thought of using drm_aperture_remove_framebuffers
> here, but this driver will be used in many different systems with many other graphics
> devices (GPU etc). Removing all the framebuffer is a bit blunt approach which may disturb
> the devices we are not intended to and which are even outside of the HyperV MMIO region.
> I feel this API use will be risky, and I would like to stick to the earlier method which
> is proven to be working for many years and we are sure it won't disturb anyone outside
> MMIO region.

But the problem with the current code is that you also remove the driver 
that covers the boot-up graphics, even if it's not even a hyperv device. 
That's why I said that you should try to detect if the hyperv device 
you're creating actually uses the screen_info when you create the device.

Set that information as device data and look it up in the hyperv-drm 
driver. If no such screen_info data is attached to the device, you don't 
have to remove conflicting framebuffers at all.

Best regards
Thomas

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

-- 
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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