On (22/12/14 14:45), Laurent Pinchart wrote:
> On Wed, Dec 14, 2022 at 12:23:41PM +0100, Ricardo Ribalda wrote:
> > UVC_MAX_STATUS_SIZE is 16, simplify the code by inlining dev->status.
>
> The reason why uvc_status is allocated dynamically is to ensure cache
> line alignment, as the USB host controller may DMA to the buffer.
Oh, that's a very subtle detail.
> > +struct uvc_status_streaming {
> > + u8 button;
> > +} __packed;
> > +
> > +struct uvc_status_control {
> > + u8 bSelector;
> > + u8 bAttribute;
> > + u8 bValue[11];
> > +} __packed;
> > +
> > +struct uvc_status {
> > + u8 bStatusType;
> > + u8 bOriginator;
> > + u8 bEvent;
> > + union {
> > + struct uvc_status_control control;
> > + struct uvc_status_streaming streaming;
> > + };
> > +} __packed;
> > +
> > struct uvc_device {
> > struct usb_device *udev;
> > struct usb_interface *intf;
> > @@ -559,7 +579,7 @@ struct uvc_device {
> > /* Status Interrupt Endpoint */
> > struct usb_host_endpoint *int_ep;
> > struct urb *int_urb;
> > - u8 *status;
> > + struct uvc_status status;
So we can do something like this maybe?
+ struct uvc_status status ____cacheline_aligned;
And this actually even improves code readability, IMHO, in a
sense that we explicitly say that it has to be cache aligned.
