Hi Ricardo,
On Thu, Dec 15, 2022 at 11:08:05AM +0200, Laurent Pinchart wrote:
> On Thu, Dec 15, 2022 at 08:59:14AM +0100, Ricardo Ribalda wrote:
> > On Thu, 15 Dec 2022 at 02:15, Sergey Senozhatsky wrote:
> > >
> > > On (22/12/14 14:37), Ricardo Ribalda wrote:
> > > [..]
> > > > +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 input_dev *input;
> > > > char input_phys[64];
> > > >
> > > > @@ -572,6 +592,12 @@ struct uvc_device {
> > > > } async_ctrl;
> > > >
> > > > struct uvc_entity *gpio_unit;
> > > > +
> > > > + /*
> > > > + * Ensure that status is aligned, making it safe to use with
> > > > + * non-coherent DMA.
> > > > + */
> > > > + struct uvc_status status __aligned(ARCH_KMALLOC_MINALIGN);
> > >
> > > ____cacheline_aligned ?
> > >
> > > I don't see anyone using ARCH_KMALLOC_MINALIGN except for slab.h
> >
> > Seems like cacheline is not good enough:
> >
> > https://github.com/torvalds/linux/commit/12c4efe3509b8018e76ea3ebda8227cb53bf5887
> > https://lore.kernel.org/all/20220405135758.774016-1-catalin.marinas@xxxxxxx/
> >
> > and ARCH_KMALLOC_MINALIGN is what we have today and is working...
> >
> > But yeah, the name for that define is not the nicest :)
> >
> > I added Jonathan Cameron, on cc, as he had to deal with something
> > similar for iio in case we are missing something
>
> I'd like to get feedback on this from DMA and USB experts. Expanding the
> CC list of the original patch would help (especially including the
> linux-usb mailing list).
Also, do we need the allocation change ? It doesn't seem to simplify the
code that much, neither in terms of lines of code
> 2 files changed, 48 insertions(+), 49 deletions(-)
nor in terms of complexity. Maybe we could keep the union and offsetof
changes, and drop the allocation change ? In any case, those are two
different changes, so I'd split them in two patches at least.
> > ps: and I thought this was an easy change :P
--
Regards,
Laurent Pinchart
