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Message-ID: <Y5nGeEdvNL3EYCxP@pendragon.ideasonboard.com>
Date: Wed, 14 Dec 2022 14:50:00 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Yunke Cao <yunkec@...omium.org>, Max Staudt <mstaudt@...gle.com>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Sergey Senozhatsky <senozhatsky@...omium.org>,
linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: [PATCH] media: uvcvideo: Do not alloc dev->status
On Wed, Dec 14, 2022 at 02:45:31PM +0200, Laurent Pinchart wrote:
> Hi Ricardo,
>
> Thank you for the patch.
>
> 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.
See
commit a31a4055473bf0a7b2b06cb2262347200d0711e1
Author: Ming Lei <tom.leiming@...il.com>
Date: Tue Sep 16 03:32:20 2008 -0300
V4L/DVB:usbvideo:don't use part of buffer for USB transfer #4
The status[] is part of uvc_device structure. We can't make sure
the address of status is at a cache-line boundary in all archs,so
status[] might share a cache-line with some fields in uvc_structure.
This can lead to some cache coherence issues(http://lwn.net/Articles/2265/).
Use dynamically allocated buffer instead.
Signed-off-by: Ming Lei <tom.leiming@...il.com>
Acked-by: Laurent Pinchart <laurent.pinchart@...net.be>
Signed-off-by: Mauro Carvalho Chehab <mchehab@...hat.com>
> > Now that we are at it, remove all the castings.
> >
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> > To: Yunke Cao <yunkec@...omium.org>
> > To: Sergey Senozhatsky <senozhatsky@...omium.org>
> > To: Max Staudt <mstaudt@...gle.com>
> > To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > To: Mauro Carvalho Chehab <mchehab@...nel.org>
> > Cc: linux-media@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > ---
> > drivers/media/usb/uvc/uvc_status.c | 69 ++++++++++++--------------------------
> > drivers/media/usb/uvc/uvcvideo.h | 22 +++++++++++-
> > 2 files changed, 42 insertions(+), 49 deletions(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
> > index 7518ffce22ed..adf63e7616c9 100644
> > --- a/drivers/media/usb/uvc/uvc_status.c
> > +++ b/drivers/media/usb/uvc/uvc_status.c
> > @@ -73,38 +73,24 @@ static void uvc_input_report_key(struct uvc_device *dev, unsigned int code,
> > /* --------------------------------------------------------------------------
> > * Status interrupt endpoint
> > */
> > -struct uvc_streaming_status {
> > - u8 bStatusType;
> > - u8 bOriginator;
> > - u8 bEvent;
> > - u8 bValue[];
> > -} __packed;
> > -
> > -struct uvc_control_status {
> > - u8 bStatusType;
> > - u8 bOriginator;
> > - u8 bEvent;
> > - u8 bSelector;
> > - u8 bAttribute;
> > - u8 bValue[];
> > -} __packed;
> > -
> > static void uvc_event_streaming(struct uvc_device *dev,
> > - struct uvc_streaming_status *status, int len)
> > + struct uvc_status *status, int len)
> > {
> > - if (len < 3) {
> > + if (len <= offsetof(struct uvc_status, bEvent)) {
> > uvc_dbg(dev, STATUS,
> > "Invalid streaming status event received\n");
> > return;
> > }
> >
> > if (status->bEvent == 0) {
> > - if (len < 4)
> > + if (len <= offsetof(struct uvc_status, streaming))
> > return;
> > +
> > uvc_dbg(dev, STATUS, "Button (intf %u) %s len %d\n",
> > status->bOriginator,
> > - status->bValue[0] ? "pressed" : "released", len);
> > - uvc_input_report_key(dev, KEY_CAMERA, status->bValue[0]);
> > + status->streaming.button ? "pressed" : "released", len);
> > + uvc_input_report_key(dev, KEY_CAMERA,
> > + status->streaming.button);
> > } else {
> > uvc_dbg(dev, STATUS, "Stream %u error event %02x len %d\n",
> > status->bOriginator, status->bEvent, len);
> > @@ -131,7 +117,7 @@ static struct uvc_control *uvc_event_entity_find_ctrl(struct uvc_entity *entity,
> > }
> >
> > static struct uvc_control *uvc_event_find_ctrl(struct uvc_device *dev,
> > - const struct uvc_control_status *status,
> > + const struct uvc_status *status,
> > struct uvc_video_chain **chain)
> > {
> > list_for_each_entry((*chain), &dev->chains, list) {
> > @@ -143,7 +129,7 @@ static struct uvc_control *uvc_event_find_ctrl(struct uvc_device *dev,
> > continue;
> >
> > ctrl = uvc_event_entity_find_ctrl(entity,
> > - status->bSelector);
> > + status->control.bSelector);
> > if (ctrl)
> > return ctrl;
> > }
> > @@ -153,7 +139,7 @@ static struct uvc_control *uvc_event_find_ctrl(struct uvc_device *dev,
> > }
> >
> > static bool uvc_event_control(struct urb *urb,
> > - const struct uvc_control_status *status, int len)
> > + const struct uvc_status *status, int len)
> > {
> > static const char *attrs[] = { "value", "info", "failure", "min", "max" };
> > struct uvc_device *dev = urb->context;
> > @@ -161,24 +147,24 @@ static bool uvc_event_control(struct urb *urb,
> > struct uvc_control *ctrl;
> >
> > if (len < 6 || status->bEvent != 0 ||
> > - status->bAttribute >= ARRAY_SIZE(attrs)) {
> > + status->control.bAttribute >= ARRAY_SIZE(attrs)) {
> > uvc_dbg(dev, STATUS, "Invalid control status event received\n");
> > return false;
> > }
> >
> > uvc_dbg(dev, STATUS, "Control %u/%u %s change len %d\n",
> > - status->bOriginator, status->bSelector,
> > - attrs[status->bAttribute], len);
> > + status->bOriginator, status->control.bSelector,
> > + attrs[status->control.bAttribute], len);
> >
> > /* Find the control. */
> > ctrl = uvc_event_find_ctrl(dev, status, &chain);
> > if (!ctrl)
> > return false;
> >
> > - switch (status->bAttribute) {
> > + switch (status->control.bAttribute) {
> > case UVC_CTRL_VALUE_CHANGE:
> > return uvc_ctrl_status_event_async(urb, chain, ctrl,
> > - status->bValue);
> > + status->control.bValue);
> >
> > case UVC_CTRL_INFO_CHANGE:
> > case UVC_CTRL_FAILURE_CHANGE:
> > @@ -214,28 +200,22 @@ static void uvc_status_complete(struct urb *urb)
> >
> > len = urb->actual_length;
> > if (len > 0) {
> > - switch (dev->status[0] & 0x0f) {
> > + switch (dev->status.bStatusType & 0x0f) {
> > case UVC_STATUS_TYPE_CONTROL: {
> > - struct uvc_control_status *status =
> > - (struct uvc_control_status *)dev->status;
> > -
> > - if (uvc_event_control(urb, status, len))
> > + if (uvc_event_control(urb, &dev->status, len))
> > /* The URB will be resubmitted in work context. */
> > return;
> > break;
> > }
> >
> > case UVC_STATUS_TYPE_STREAMING: {
> > - struct uvc_streaming_status *status =
> > - (struct uvc_streaming_status *)dev->status;
> > -
> > - uvc_event_streaming(dev, status, len);
> > + uvc_event_streaming(dev, &dev->status, len);
> > break;
> > }
> >
> > default:
> > uvc_dbg(dev, STATUS, "Unknown status event type %u\n",
> > - dev->status[0]);
> > + dev->status.bStatusType);
> > break;
> > }
> > }
> > @@ -259,15 +239,9 @@ int uvc_status_init(struct uvc_device *dev)
> >
> > uvc_input_init(dev);
> >
> > - dev->status = kzalloc(UVC_MAX_STATUS_SIZE, GFP_KERNEL);
> > - if (dev->status == NULL)
> > - return -ENOMEM;
> > -
> > dev->int_urb = usb_alloc_urb(0, GFP_KERNEL);
> > - if (dev->int_urb == NULL) {
> > - kfree(dev->status);
> > + if (!dev->int_urb)
> > return -ENOMEM;
> > - }
> >
> > pipe = usb_rcvintpipe(dev->udev, ep->desc.bEndpointAddress);
> >
> > @@ -281,7 +255,7 @@ int uvc_status_init(struct uvc_device *dev)
> > interval = fls(interval) - 1;
> >
> > usb_fill_int_urb(dev->int_urb, dev->udev, pipe,
> > - dev->status, UVC_MAX_STATUS_SIZE, uvc_status_complete,
> > + &dev->status, sizeof(dev->status), uvc_status_complete,
> > dev, interval);
> >
> > return 0;
> > @@ -296,7 +270,6 @@ void uvc_status_unregister(struct uvc_device *dev)
> > void uvc_status_cleanup(struct uvc_device *dev)
> > {
> > usb_free_urb(dev->int_urb);
> > - kfree(dev->status);
> > }
> >
> > int uvc_status_start(struct uvc_device *dev, gfp_t flags)
> > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > index df93db259312..cdd2e328acc2 100644
> > --- a/drivers/media/usb/uvc/uvcvideo.h
> > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > @@ -527,6 +527,26 @@ struct uvc_device_info {
> > const struct uvc_control_mapping **mappings;
> > };
> >
> > +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;
> > struct input_dev *input;
> > char input_phys[64];
> >
> >
> > ---
> > base-commit: 0ec5a38bf8499f403f81cb81a0e3a60887d1993c
> > change-id: 20221214-uvc-status-alloc-93becb783898
--
Regards,
Laurent Pinchart
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