[PATCH v4 0/1] Support per-head resolutions with virtio-gpu

[PATCH v4 0/1] Support per-head resolutions with virtio-gpu

[Andrew Keesler]

In 454f4b0f, we started down the path of supporting separate
configurations per display head (e.g., you have 2 heads - one with
EDID name "AAA" and the other with EDID name "BBB").

In this change, we add resolution to this configuration surface (e.g.,
you have 2 heads - one with resolution 111x222 and the other with
resolution 333x444).

  -display vnc=localhost:0,id=aaa,display=vga,head=0 \
  -display vnc=localhost:1,id=bbb,display=vga,head=1 \
  -device '{"driver":"virtio-vga",
            "max_outputs":2,
            "id":"vga",
            "outputs":[
              {
                 "name":"AAA",
                 "xres":111,
                 "yres":222
              },
              {
                 "name":"BBB",
                 "xres":333,
                 "yres":444
              }
            ]}'

Here is the behavior matrix of the current resolution configuration
surface (xres/yres) with the new resolution configuration surface
(outputs[i].xres/yres).

Case: !(xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
Behavior: current behavior - outputs[0] enabled with default xres/yres

Case: (xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
Behavior: current behavior - outputs[0] enabled with xres/yres

Case: !(xres || yres) && (outputs[i].has_xres && outputs[i].has_yres)
Behavior: new behavior - outputs[i] enabled with outputs[i].xres/yres

Case: (xres || yres) && (outputs[i].has_xres && outputs[i].has_yres)
Behavior: new behavior - outputs[i] enabled with outputs[i].xres/yres

Changelist:
* v4: changes after dropped from pull request
  * rebase against master (3b5fe75e2c)
  * use @NAME (@xres/@yres) in qapi/virtio.json docs
  * documented behavior when only one or none of @xres/@yres is set
* v3: changes after v2 review
  * fix new resolution configuration logic (&& instead of ||)
  * correct use of api machinery (has_*)
  * move documentation to QMP API
* v2: changes after v1 review + 10.2 rebase
  * updated code, commit message, and cover letter to match new res config logic
  * marked new VirtIOGPUOutput fields as optional and since 10.2
* v1: initial patch

Andrew Keesler (1):
  Support per-head resolutions with virtio-gpu

 hw/display/virtio-gpu-base.c | 10 ++++++++++
 qapi/virtio.json             | 13 +++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

-- 
2.52.0.457.g6b5491de43-goog

[PATCH v4 1/1] Support per-head resolutions with virtio-gpu

[Andrew Keesler]

In 454f4b0f, we started down the path of supporting separate
configurations per display head (e.g., you have 2 heads - one with
EDID name "AAA" and the other with EDID name "BBB").

In this change, we add resolution to this configuration surface (e.g.,
you have 2 heads - one with resolution 111x222 and the other with
resolution 333x444).

  -display vnc=localhost:0,id=aaa,display=vga,head=0 \
  -display vnc=localhost:1,id=bbb,display=vga,head=1 \
  -device '{"driver":"virtio-vga",
            "max_outputs":2,
            "id":"vga",
            "outputs":[
              {
                 "name":"AAA",
                 "xres":111,
                 "yres":222
              },
              {
                 "name":"BBB",
                 "xres":333,
                 "yres":444
              }
            ]}'

Here is the behavior matrix of the current resolution configuration
surface (xres/yres) with the new resolution configuration surface
(outputs[i].xres/yres).

Case: !(xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
Behavior: current behavior - outputs[0] enabled with default xres/yres

Case: (xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
Behavior: current behavior - outputs[0] enabled with xres/yres

Case: !(xres || yres) && (outputs[i].has_xres && outputs[i].has_yres)
Behavior: new behavior - outputs[i] enabled with outputs[i].xres/yres

Case: (xres || yres) && (outputs[i].has_xres && outputs[i].has_yres)
Behavior: new behavior - outputs[i] enabled with outputs[i].xres/yres

Signed-off-by: Andrew Keesler <ankeesler@google.com>
---
 hw/display/virtio-gpu-base.c | 10 ++++++++++
 qapi/virtio.json             | 13 +++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/hw/display/virtio-gpu-base.c b/hw/display/virtio-gpu-base.c
index 7269477a1c..6adb5312a4 100644
--- a/hw/display/virtio-gpu-base.c
+++ b/hw/display/virtio-gpu-base.c
@@ -233,6 +233,16 @@ virtio_gpu_base_device_realize(DeviceState *qdev,
     g->req_state[0].width = g->conf.xres;
     g->req_state[0].height = g->conf.yres;
 
+    for (output_idx = 0, node = g->conf.outputs;
+         node && output_idx < g->conf.max_outputs;
+         output_idx++, node = node->next) {
+        if (node->value->has_xres && node->value->has_yres) {
+            g->enabled_output_bitmask |= (1 << output_idx);
+            g->req_state[output_idx].width = node->value->xres;
+            g->req_state[output_idx].height = node->value->yres;
+        }
+    }
+
     g->hw_ops = &virtio_gpu_ops;
     for (i = 0; i < g->conf.max_outputs; i++) {
         g->scanout[i].con =
diff --git a/qapi/virtio.json b/qapi/virtio.json
index cd67c4f52e..c1a1fb4997 100644
--- a/qapi/virtio.json
+++ b/qapi/virtio.json
@@ -970,15 +970,24 @@
 ##
 # @VirtIOGPUOutput:
 #
-# Describes configuration of a VirtIO GPU output.
+# Describes configuration of a VirtIO GPU output.  If both @xres and
+# @yres are set, they take precedence over root virtio-gpu
+# resolution configuration and enable the corresponding output.  If
+# only one or none of @xres or @yres is set, root virtio-gpu
+# resolution configuration takes precedence and only the first output
+# is enabled.
 #
 # @name: the name of the output
 #
+# @xres: horizontal resolution of the output in pixels (since 10.2)
+#
+# @yres: vertical resolution of the output in pixels (since 10.2)
+#
 # Since: 10.1
 ##
 
 { 'struct': 'VirtIOGPUOutput',
-  'data': { 'name': 'str' } }
+  'data': { 'name': 'str', '*xres': 'uint16', '*yres': 'uint16' } }
 
 ##
 # @DummyVirtioForceArrays:
-- 
2.52.0.457.g6b5491de43-goog

Re: [PATCH v4 1/1] Support per-head resolutions with virtio-gpu

[Andrew Keesler]

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Note - we use "xres" and "yres" (instead of, say, "width" and "height")
to match analogous virtio_gpu_base_conf.xres/yres.

On Fri, Jan 9, 2026 at 3:27 PM Andrew Keesler <ankeesler@google.com> wrote:

> In 454f4b0f, we started down the path of supporting separate
> configurations per display head (e.g., you have 2 heads - one with
> EDID name "AAA" and the other with EDID name "BBB").
>
> In this change, we add resolution to this configuration surface (e.g.,
> you have 2 heads - one with resolution 111x222 and the other with
> resolution 333x444).
>
>   -display vnc=localhost:0,id=aaa,display=vga,head=0 \
>   -display vnc=localhost:1,id=bbb,display=vga,head=1 \
>   -device '{"driver":"virtio-vga",
>             "max_outputs":2,
>             "id":"vga",
>             "outputs":[
>               {
>                  "name":"AAA",
>                  "xres":111,
>                  "yres":222
>               },
>               {
>                  "name":"BBB",
>                  "xres":333,
>                  "yres":444
>               }
>             ]}'
>
> Here is the behavior matrix of the current resolution configuration
> surface (xres/yres) with the new resolution configuration surface
> (outputs[i].xres/yres).
>
> Case: !(xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
> Behavior: current behavior - outputs[0] enabled with default xres/yres
>
> Case: (xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
> Behavior: current behavior - outputs[0] enabled with xres/yres
>
> Case: !(xres || yres) && (outputs[i].has_xres && outputs[i].has_yres)
> Behavior: new behavior - outputs[i] enabled with outputs[i].xres/yres
>
> Case: (xres || yres) && (outputs[i].has_xres && outputs[i].has_yres)
> Behavior: new behavior - outputs[i] enabled with outputs[i].xres/yres
>
> Signed-off-by: Andrew Keesler <ankeesler@google.com>
> ---
>  hw/display/virtio-gpu-base.c | 10 ++++++++++
>  qapi/virtio.json             | 13 +++++++++++--
>  2 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/hw/display/virtio-gpu-base.c b/hw/display/virtio-gpu-base.c
> index 7269477a1c..6adb5312a4 100644
> --- a/hw/display/virtio-gpu-base.c
> +++ b/hw/display/virtio-gpu-base.c
> @@ -233,6 +233,16 @@ virtio_gpu_base_device_realize(DeviceState *qdev,
>      g->req_state[0].width = g->conf.xres;
>      g->req_state[0].height = g->conf.yres;
>
> +    for (output_idx = 0, node = g->conf.outputs;
> +         node && output_idx < g->conf.max_outputs;
> +         output_idx++, node = node->next) {
> +        if (node->value->has_xres && node->value->has_yres) {
> +            g->enabled_output_bitmask |= (1 << output_idx);
> +            g->req_state[output_idx].width = node->value->xres;
> +            g->req_state[output_idx].height = node->value->yres;
> +        }
> +    }
> +
>      g->hw_ops = &virtio_gpu_ops;
>      for (i = 0; i < g->conf.max_outputs; i++) {
>          g->scanout[i].con =
> diff --git a/qapi/virtio.json b/qapi/virtio.json
> index cd67c4f52e..c1a1fb4997 100644
> --- a/qapi/virtio.json
> +++ b/qapi/virtio.json
> @@ -970,15 +970,24 @@
>  ##
>  # @VirtIOGPUOutput:
>  #
> -# Describes configuration of a VirtIO GPU output.
> +# Describes configuration of a VirtIO GPU output.  If both @xres and
> +# @yres are set, they take precedence over root virtio-gpu
> +# resolution configuration and enable the corresponding output.  If
> +# only one or none of @xres or @yres is set, root virtio-gpu
> +# resolution configuration takes precedence and only the first output
> +# is enabled.
>  #
>  # @name: the name of the output
>  #
> +# @xres: horizontal resolution of the output in pixels (since 10.2)
> +#
> +# @yres: vertical resolution of the output in pixels (since 10.2)
> +#
>  # Since: 10.1
>  ##
>
>  { 'struct': 'VirtIOGPUOutput',
> -  'data': { 'name': 'str' } }
> +  'data': { 'name': 'str', '*xres': 'uint16', '*yres': 'uint16' } }
>
>  ##
>  # @DummyVirtioForceArrays:
> --
> 2.52.0.457.g6b5491de43-goog
>
>

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Re: [PATCH v4 1/1] Support per-head resolutions with virtio-gpu

[Andrew Keesler]

[-- Attachment #1: Type: text/plain, Size: 4509 bytes --]

Gentle request for review.

This change was previously queued, and then dropped from a PR:

  https://mail.gnu.org/archive/html/qemu-devel/2025-10/msg04960.html

This v4 PATCH addresses those comments.



On Fri, Jan 9, 2026 at 3:31 PM Andrew Keesler <ankeesler@google.com> wrote:

> Note - we use "xres" and "yres" (instead of, say, "width" and "height")
> to match analogous virtio_gpu_base_conf.xres/yres.
>
> On Fri, Jan 9, 2026 at 3:27 PM Andrew Keesler <ankeesler@google.com>
> wrote:
>
>> In 454f4b0f, we started down the path of supporting separate
>> configurations per display head (e.g., you have 2 heads - one with
>> EDID name "AAA" and the other with EDID name "BBB").
>>
>> In this change, we add resolution to this configuration surface (e.g.,
>> you have 2 heads - one with resolution 111x222 and the other with
>> resolution 333x444).
>>
>>   -display vnc=localhost:0,id=aaa,display=vga,head=0 \
>>   -display vnc=localhost:1,id=bbb,display=vga,head=1 \
>>   -device '{"driver":"virtio-vga",
>>             "max_outputs":2,
>>             "id":"vga",
>>             "outputs":[
>>               {
>>                  "name":"AAA",
>>                  "xres":111,
>>                  "yres":222
>>               },
>>               {
>>                  "name":"BBB",
>>                  "xres":333,
>>                  "yres":444
>>               }
>>             ]}'
>>
>> Here is the behavior matrix of the current resolution configuration
>> surface (xres/yres) with the new resolution configuration surface
>> (outputs[i].xres/yres).
>>
>> Case: !(xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
>> Behavior: current behavior - outputs[0] enabled with default xres/yres
>>
>> Case: (xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
>> Behavior: current behavior - outputs[0] enabled with xres/yres
>>
>> Case: !(xres || yres) && (outputs[i].has_xres && outputs[i].has_yres)
>> Behavior: new behavior - outputs[i] enabled with outputs[i].xres/yres
>>
>> Case: (xres || yres) && (outputs[i].has_xres && outputs[i].has_yres)
>> Behavior: new behavior - outputs[i] enabled with outputs[i].xres/yres
>>
>> Signed-off-by: Andrew Keesler <ankeesler@google.com>
>> ---
>>  hw/display/virtio-gpu-base.c | 10 ++++++++++
>>  qapi/virtio.json             | 13 +++++++++++--
>>  2 files changed, 21 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/display/virtio-gpu-base.c b/hw/display/virtio-gpu-base.c
>> index 7269477a1c..6adb5312a4 100644
>> --- a/hw/display/virtio-gpu-base.c
>> +++ b/hw/display/virtio-gpu-base.c
>> @@ -233,6 +233,16 @@ virtio_gpu_base_device_realize(DeviceState *qdev,
>>      g->req_state[0].width = g->conf.xres;
>>      g->req_state[0].height = g->conf.yres;
>>
>> +    for (output_idx = 0, node = g->conf.outputs;
>> +         node && output_idx < g->conf.max_outputs;
>> +         output_idx++, node = node->next) {
>> +        if (node->value->has_xres && node->value->has_yres) {
>> +            g->enabled_output_bitmask |= (1 << output_idx);
>> +            g->req_state[output_idx].width = node->value->xres;
>> +            g->req_state[output_idx].height = node->value->yres;
>> +        }
>> +    }
>> +
>>      g->hw_ops = &virtio_gpu_ops;
>>      for (i = 0; i < g->conf.max_outputs; i++) {
>>          g->scanout[i].con =
>> diff --git a/qapi/virtio.json b/qapi/virtio.json
>> index cd67c4f52e..c1a1fb4997 100644
>> --- a/qapi/virtio.json
>> +++ b/qapi/virtio.json
>> @@ -970,15 +970,24 @@
>>  ##
>>  # @VirtIOGPUOutput:
>>  #
>> -# Describes configuration of a VirtIO GPU output.
>> +# Describes configuration of a VirtIO GPU output.  If both @xres and
>> +# @yres are set, they take precedence over root virtio-gpu
>> +# resolution configuration and enable the corresponding output.  If
>> +# only one or none of @xres or @yres is set, root virtio-gpu
>> +# resolution configuration takes precedence and only the first output
>> +# is enabled.
>>  #
>>  # @name: the name of the output
>>  #
>> +# @xres: horizontal resolution of the output in pixels (since 10.2)
>> +#
>> +# @yres: vertical resolution of the output in pixels (since 10.2)
>> +#
>>  # Since: 10.1
>>  ##
>>
>>  { 'struct': 'VirtIOGPUOutput',
>> -  'data': { 'name': 'str' } }
>> +  'data': { 'name': 'str', '*xres': 'uint16', '*yres': 'uint16' } }
>>
>>  ##
>>  # @DummyVirtioForceArrays:
>> --
>> 2.52.0.457.g6b5491de43-goog
>>
>>

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Re: [PATCH v4 1/1] Support per-head resolutions with virtio-gpu

[Markus Armbruster]

Sorry for the delay.  Recovering from the coughing plague.

Andrew Keesler <ankeesler@google.com> writes:

> In 454f4b0f, we started down the path of supporting separate
> configurations per display head (e.g., you have 2 heads - one with
> EDID name "AAA" and the other with EDID name "BBB").
>
> In this change, we add resolution to this configuration surface (e.g.,
> you have 2 heads - one with resolution 111x222 and the other with
> resolution 333x444).
>
>   -display vnc=localhost:0,id=aaa,display=vga,head=0 \
>   -display vnc=localhost:1,id=bbb,display=vga,head=1 \
>   -device '{"driver":"virtio-vga",
>             "max_outputs":2,
>             "id":"vga",
>             "outputs":[
>               {
>                  "name":"AAA",
>                  "xres":111,
>                  "yres":222
>               },
>               {
>                  "name":"BBB",
>                  "xres":333,
>                  "yres":444
>               }
>             ]}'
>
> Here is the behavior matrix of the current resolution configuration
> surface (xres/yres) with the new resolution configuration surface
> (outputs[i].xres/yres).
>
> Case: !(xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
> Behavior: current behavior - outputs[0] enabled with default xres/yres
>
> Case: (xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
> Behavior: current behavior - outputs[0] enabled with xres/yres
>
> Case: !(xres || yres) && (outputs[i].has_xres && outputs[i].has_yres)
> Behavior: new behavior - outputs[i] enabled with outputs[i].xres/yres
>
> Case: (xres || yres) && (outputs[i].has_xres && outputs[i].has_yres)
> Behavior: new behavior - outputs[i] enabled with outputs[i].xres/yres
>
> Signed-off-by: Andrew Keesler <ankeesler@google.com>

[...]

> diff --git a/qapi/virtio.json b/qapi/virtio.json
> index cd67c4f52e..c1a1fb4997 100644
> --- a/qapi/virtio.json
> +++ b/qapi/virtio.json
> @@ -970,15 +970,24 @@
>  ##
>  # @VirtIOGPUOutput:
>  #
> -# Describes configuration of a VirtIO GPU output.
> +# Describes configuration of a VirtIO GPU output.  If both @xres and
> +# @yres are set, they take precedence over root virtio-gpu
> +# resolution configuration and enable the corresponding output.  If
> +# only one or none of @xres or @yres is set, root virtio-gpu
> +# resolution configuration takes precedence and only the first output
> +# is enabled.

So when exactly one of @xres or @yes is present, it's silently ignored?

>  #
>  # @name: the name of the output
>  #
> +# @xres: horizontal resolution of the output in pixels (since 10.2)
> +#
> +# @yres: vertical resolution of the output in pixels (since 10.2)

(since 11.0)

> +#
>  # Since: 10.1
>  ##
>  
>  { 'struct': 'VirtIOGPUOutput',
> -  'data': { 'name': 'str' } }
> +  'data': { 'name': 'str', '*xres': 'uint16', '*yres': 'uint16' } }
>  
>  ##
>  # @DummyVirtioForceArrays:

Re: [PATCH v4 1/1] Support per-head resolutions with virtio-gpu

[Markus Armbruster]

Andrew Keesler <ankeesler@google.com> writes:

> Note - we use "xres" and "yres" (instead of, say, "width" and "height")
> to match analogous virtio_gpu_base_conf.xres/yres.

Mentioning this in the commit message wouldn't hurt.

Re: [PATCH v4 1/1] Support per-head resolutions with virtio-gpu

[Andrew Keesler]

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> So when exactly one of @xres or @yes is present, it's silently ignored?

That is the currently proposed behavior, yes.

Here is the related review comment.

  https://mail.gnu.org/archive/html/qemu-devel/2025-08/msg04584.html

WDYT?

> (since 11.0)

ACK, fixed in next patch.

> Mentioning this in the commit message wouldn't hurt.

ACK, fixed in next patch.

> Recovering from the coughing plague.

Hope you feel better.


On Wed, Feb 4, 2026 at 7:47 AM Markus Armbruster <armbru@redhat.com> wrote:

> Andrew Keesler <ankeesler@google.com> writes:
>
> > Note - we use "xres" and "yres" (instead of, say, "width" and "height")
> > to match analogous virtio_gpu_base_conf.xres/yres.
>
> Mentioning this in the commit message wouldn't hurt.
>
>

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Re: [PATCH v4 1/1] Support per-head resolutions with virtio-gpu

[Markus Armbruster]

Andrew Keesler <ankeesler@google.com> writes:

>> So when exactly one of @xres or @yes is present, it's silently ignored?
>
> That is the currently proposed behavior, yes.
>
> Here is the related review comment.
>
>   https://mail.gnu.org/archive/html/qemu-devel/2025-08/msg04584.html
>
> WDYT?

I think nonsensical configuration should be an error.

>> (since 11.0)
>
> ACK, fixed in next patch.
>
>> Mentioning this in the commit message wouldn't hurt.
>
> ACK, fixed in next patch.
>
>> Recovering from the coughing plague.
>
> Hope you feel better.

Much improved, thanks!

[...]