Re: [PATCH v3 6/6] usb: gadget: uvc: add configfs option for sg support

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Hi Michael

On 18/10/2022 15:04, Michael Grzeschik wrote:
Hi Dan!
Hi Dan!

On Tue, Oct 18, 2022 at 02:27:13PM +0100, Dan Scally wrote:
Hi Dan

On 17/10/2022 21:54, Dan Vacura wrote:
The scatter gather support doesn't appear to work well with some UDC hw.
Add the ability to turn on the feature depending on the controller in
use.

Signed-off-by: Dan Vacura <w36195@xxxxxxxxxxxx>


Nitpick: I would call it use_sg everywhere, but either way:

Or even only "scatter_gather". How does that sound?


Reviewed-by: Daniel Scally <dan.scally@xxxxxxxxxxxxxxxx>

Tested-by: Daniel Scally <dan.scally@xxxxxxxxxxxxxxxx>

---
V1 -> V2:
- no change, new patch in serie
V2 -> V3:
- default on, same as baseline

 Documentation/ABI/testing/configfs-usb-gadget-uvc | 1 +
 Documentation/usb/gadget-testing.rst              | 2 ++
 drivers/usb/gadget/function/f_uvc.c               | 2 ++
 drivers/usb/gadget/function/u_uvc.h               | 1 +
 drivers/usb/gadget/function/uvc_configfs.c        | 2 ++
 drivers/usb/gadget/function/uvc_queue.c           | 4 ++--
 6 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/testing/configfs-usb-gadget-uvc b/Documentation/ABI/testing/configfs-usb-gadget-uvc
index 5dfaa3f7f6a4..839a75fc28ee 100644
--- a/Documentation/ABI/testing/configfs-usb-gadget-uvc
+++ b/Documentation/ABI/testing/configfs-usb-gadget-uvc
@@ -9,6 +9,7 @@ Description:    UVC function directory
         streaming_interval    1..16
         function_name        string [32]
         req_int_skip_div    unsigned int
+        sg_supported        0..1
         ===================    =============================
 What: /config/usb-gadget/gadget/functions/uvc.name/control
diff --git a/Documentation/usb/gadget-testing.rst b/Documentation/usb/gadget-testing.rst
index f9b5a09be1f4..8e3072d6a590 100644
--- a/Documentation/usb/gadget-testing.rst
+++ b/Documentation/usb/gadget-testing.rst
@@ -796,6 +796,8 @@ The uvc function provides these attributes in its function directory:
     function_name       name of the interface
     req_int_skip_div    divisor of total requests to aid in calculating
                 interrupt frequency, 0 indicates all interrupt
+    sg_supported        allow for scatter gather to be used if the UDC
+                hw supports it
     =================== ================================================  There are also "control" and "streaming" subdirectories, each of which contain diff --git a/drivers/usb/gadget/function/f_uvc.c b/drivers/usb/gadget/function/f_uvc.c
index e40ca26b9c55..d08ebe3ffeb2 100644
--- a/drivers/usb/gadget/function/f_uvc.c
+++ b/drivers/usb/gadget/function/f_uvc.c
@@ -656,6 +656,7 @@ uvc_function_bind(struct usb_configuration *c, struct usb_function *f)
                 (opts->streaming_maxburst + 1));
     uvc->config_skip_int_div = opts->req_int_skip_div;
+    uvc->video.queue.use_sg = opts->sg_supported;

Why do you set this here?

     /* Allocate endpoints. */
     ep = usb_ep_autoconfig(cdev->gadget, &uvc_control_ep);
@@ -875,6 +876,7 @@ static struct usb_function_instance *uvc_alloc_inst(void)
     opts->streaming_interval = 1;
     opts->streaming_maxpacket = 1024;
     opts->req_int_skip_div = 4;
+    opts->sg_supported = 1;
     snprintf(opts->function_name, sizeof(opts->function_name), "UVC Camera");
     ret = uvcg_attach_configfs(opts);
diff --git a/drivers/usb/gadget/function/u_uvc.h b/drivers/usb/gadget/function/u_uvc.h
index 6f73bd5638ed..5ccced629925 100644
--- a/drivers/usb/gadget/function/u_uvc.h
+++ b/drivers/usb/gadget/function/u_uvc.h
@@ -25,6 +25,7 @@ struct f_uvc_opts {
     unsigned int                    streaming_maxpacket;
     unsigned int                    streaming_maxburst;
     unsigned int                    req_int_skip_div;
+    unsigned int                    sg_supported;
     unsigned int                    control_interface;
     unsigned int                    streaming_interface;
diff --git a/drivers/usb/gadget/function/uvc_configfs.c b/drivers/usb/gadget/function/uvc_configfs.c
index 419e926ab57e..3784c0e02d01 100644
--- a/drivers/usb/gadget/function/uvc_configfs.c
+++ b/drivers/usb/gadget/function/uvc_configfs.c
@@ -2351,6 +2351,7 @@ UVCG_OPTS_ATTR(streaming_interval, streaming_interval, 16);
 UVCG_OPTS_ATTR(streaming_maxpacket, streaming_maxpacket, 3072);
 UVCG_OPTS_ATTR(streaming_maxburst, streaming_maxburst, 15);
 UVCG_OPTS_ATTR(req_int_skip_div, req_int_skip_div, UINT_MAX);
+UVCG_OPTS_ATTR(sg_supported, sg_supported, 1);
 #undef UVCG_OPTS_ATTR
@@ -2401,6 +2402,7 @@ static struct configfs_attribute *uvc_attrs[] = {
     &f_uvc_opts_attr_streaming_maxpacket,
     &f_uvc_opts_attr_streaming_maxburst,
     &f_uvc_opts_attr_req_int_skip_div,
+    &f_uvc_opts_attr_sg_supported,
     &f_uvc_opts_string_attr_function_name,
     NULL,
 };
diff --git a/drivers/usb/gadget/function/uvc_queue.c b/drivers/usb/gadget/function/uvc_queue.c
index 02559906a55a..3c7aa5c4bba2 100644
--- a/drivers/usb/gadget/function/uvc_queue.c
+++ b/drivers/usb/gadget/function/uvc_queue.c
@@ -149,11 +149,11 @@ int uvcg_queue_init(struct uvc_video_queue *queue, struct device *dev, enum v4l2
     queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
     queue->queue.ops = &uvc_queue_qops;
     queue->queue.lock = lock;
-    if (cdev->gadget->sg_supported) {
+    if (queue->use_sg && cdev->gadget->sg_supported) {
         queue->queue.mem_ops = &vb2_dma_sg_memops;
-        queue->use_sg = 1;
     } else {
         queue->queue.mem_ops = &vb2_vmalloc_memops;
+        queue->use_sg = false;

I am unsure, but can you actually not always use vb2_dma_sg_memops.


We have problems with this on the imx8mp EVK, because it doesn't account for dma-range properties in device tree and so will attempt to allocate memory outside the 4GB range that a DWC3 can access. The allocation attempts to fall back on the swiotlb, but that's slow even if it works...and it can fail and return -ENOMEM if the swiotlb is too small.


Probably some future work needs to fix the vb2_dma_sg_memops to take those dma constraints into account, but for now I wouldn't force its use.


With my last patch we always set buf->mem to vb2_plane_vaddr(vb, 0);

https://lore.kernel.org/linux-usb/20221017221141.3134818-1-m.grzeschik@xxxxxxxxxxxxxx/T/#u


The condition to decide if encode_isoc_sg or encode_isoc should then
remain the last place to switch between sg or not. I would hook the
userspace decision in here.

You can also directly get to opts->scatter_gather by using

    struct f_uvc_opts *opts = fi_to_f_uvc_opts(uvc->func.fi);

in the function uvcg_video_enable.

     }
     queue->queue.timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_COPY


Thanks,
Michael




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