Re: [RFC PATCH 5/5] input/hid: apply multiplier scaling with residual accumulation

[Helge Deller <deller@gmx.de>]

On 3/31/26 19:08, Soumyajyotii Ssarkar wrote:
> Implement multiplier-based scaling with residual accumulation for
> fine-grained mouse wheel and pan sensitivity control in report mode.
> 
> Applies divisor based scaling (1, 4, 8, 16) based on negotiated
> multiplier values.
> Then uses residual based approach to prevent precision loss:
> 
>    residual += delta
>    output = residual / divisor
>    residual -= output * divisor
> 
> Residual state preserved across VM migrations via VMState.
> 
> Signed-off-by: Soumyajyotii Ssarkar <soumyajyotisarkar23@gmail.com>
> ---
>   hw/input/hid.c         | 60 ++++++++++++++++++++++++++++++++++++++++++
>   include/hw/input/hid.h |  2 ++
>   2 files changed, 62 insertions(+)
> 
> diff --git a/hw/input/hid.c b/hw/input/hid.c
> index d0b7af7c13..9b800faeb0 100644
> --- a/hw/input/hid.c
> +++ b/hw/input/hid.c
> @@ -365,6 +365,7 @@ void hid_pointer_activate(HIDState *hs)
>   int hid_pointer_poll(HIDState *hs, uint8_t *buf, int len)
>   {
>       int dx, dy, dz, pan, l;
> +    int wheel_divisor, pan_divisor;
>       int index;
>       HIDPointerEvent *e;
> 
> @@ -392,6 +393,54 @@ int hid_pointer_poll(HIDState *hs, uint8_t *buf, int len)
>       e->pan -= pan;
> 
> 
> +    if (hs->kind == HID_MOUSE && hs->protocol != 0) {

shouldn't this better be "hs->protocol == 1" ?


> +        switch (hs->ptr.wheel_multiplier & 0x03) {
> +        case 0:
> +            wheel_divisor = 1;
> +            break;
> +        case 1:
> +            wheel_divisor = 4;
> +            break;
> +        case 2:
> +            wheel_divisor = 8;
> +            break;
> +        default:
> +            wheel_divisor = 16;
> +            break;
> +        }
> +
> +        switch (hs->ptr.pan_multiplier & 0x03) {
> +        case 0:
> +            pan_divisor = 1;
> +            break;
> +        case 1:
> +            pan_divisor = 4;
> +            break;
> +        case 2:
> +            pan_divisor = 8;
> +            break;
> +        default:
> +            pan_divisor = 16;
> +            break;
> +        }
> +
> +        if (wheel_divisor > 1) {
> +            hs->ptr.wheel_residual += dz;
> +            dz = hs->ptr.wheel_residual / wheel_divisor;
> +            hs->ptr.wheel_residual -= dz * wheel_divisor;
> +        } else {
> +            hs->ptr.wheel_residual = 0;
> +        }

maybe instead of the whole above: ?

	if (hs->ptr.wheel_multiplier & 0x03) {
             wheel_divisor = 2 << (hs->ptr.wheel_multiplier & 0x03);
             hs->ptr.wheel_residual += dz;
             dz = hs->ptr.wheel_residual / wheel_divisor;
             hs->ptr.wheel_residual -= dz * wheel_divisor;
         } else {
             hs->ptr.wheel_residual = 0;
         }

> +
> +        if (pan_divisor > 1) {
> +            hs->ptr.pan_residual += pan;
> +            pan = hs->ptr.pan_residual / pan_divisor;
> +            hs->ptr.pan_residual -= pan * pan_divisor;
> +        } else {
> +            hs->ptr.pan_residual = 0;
> +        }

same here.


> +    }
> +
>       if (hs->n &&
>           !e->dz &&
>           !e->pan &&
> @@ -405,6 +454,7 @@ int hid_pointer_poll(HIDState *hs, uint8_t *buf, int len)
>       dz = 0 - dz;
>       pan = 0 - pan;
>       l = 0;
> +

drop this change.

>       switch (hs->kind) {
>       case HID_MOUSE:
>           if (hs->protocol == 0) {
> @@ -528,6 +578,11 @@ void hid_reset(HIDState *hs)
>       case HID_MOUSE:
>       case HID_TABLET:
>           memset(hs->ptr.queue, 0, sizeof(hs->ptr.queue));
> +        hs->ptr.mouse_grabbed = 0;
> +        hs->ptr.wheel_multiplier = 0;
> +        hs->ptr.pan_multiplier = 0;
> +        hs->ptr.wheel_residual = 0;
> +        hs->ptr.pan_residual = 0;

and move that in an own patch.

Otherwise the patch seems ok.
I suggest you resend the series with the proposed changes and
make sure it applies against git head.

Thanks!
Helge