Re: [PATCH v3 6/6] usb: gadget: function: Add Generic USB Display support

[Felipe Balbi <balbi@kernel.org>]

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Hi,

I missed this completely until now.
Noralf Trønnes <noralf@tronnes.org> writes:
> This adds the gadget side support for the Generic USB Display. It presents
> a DRM display device as a USB Display configured through configfs.
>
> The display is implemented as a vendor type USB interface with one bulk
> out endpoint. The protocol is implemented using control requests.
> lz4 compressed framebuffer data/pixels are sent over the bulk endpoint.
>
> The DRM part of the gadget is placed in the DRM subsystem since it reaches
> into the DRM internals.

First and foremost, could this be done in userspace using the raw gadget
or f_fs?

> diff --git a/drivers/usb/gadget/function/f_gud_drm.c b/drivers/usb/gadget/function/f_gud_drm.c
> new file mode 100644
> index 000000000000..9a2d6bb9739f
> --- /dev/null
> +++ b/drivers/usb/gadget/function/f_gud_drm.c
> @@ -0,0 +1,678 @@
> +struct f_gud_drm {
> +	struct usb_function func;
> +	struct work_struct worker;

why do you need a worker?

> +	size_t max_buffer_size;
> +	void *ctrl_req_buf;
> +
> +	u8 interface_id;
> +	struct usb_request *ctrl_req;
> +
> +	struct usb_ep *bulk_ep;
> +	struct usb_request *bulk_req;

single request? Don't you want to amortize the latency of
queue->complete by using a series of requests?

> +	struct gud_drm_gadget *gdg;
> +
> +	spinlock_t lock; /* Protects the following members: */
> +	bool ctrl_pending;
> +	bool status_pending;
> +	bool bulk_pending;
> +	bool disable_pending;

could this be a single u32 with #define'd flags? That would be atomic,
right?

> +	u8 errno;

a global per-function error? Why?

> +	u16 request;
> +	u16 value;

also why? Looks odd

> +};
> +
> +static inline struct f_gud_drm *func_to_f_gud_drm(struct usb_function *f)

let the compiler inline for you

> +{
> +	return container_of(f, struct f_gud_drm, func);

could be a macro, but okay.

> +static inline struct f_gud_drm_opts *fi_to_f_gud_drm_opts(const struct usb_function_instance *fi)

ditto

> +{
> +	return container_of(fi, struct f_gud_drm_opts, func_inst);

ditto

> +}
> +
> +static inline struct f_gud_drm_opts *ci_to_f_gud_drm_opts(struct config_item *item)

ditto

> +{
> +	return container_of(to_config_group(item), struct f_gud_drm_opts,
> +			    func_inst.group);

ditto

> +}
> +
> +#define F_MUD_DEFINE_BULK_ENDPOINT_DESCRIPTOR(name, addr, size)	\
> +	static struct usb_endpoint_descriptor name = {		\

const? Also, please check all the others

> +static void f_gud_drm_bulk_complete(struct usb_ep *ep, struct usb_request *req)
> +{
> +	struct f_gud_drm *fgd = req->context;
> +	unsigned long flags;
> +
> +	if (req->status || req->actual != req->length)
> +		return;

so, if we complete with an erroneous status or a short packet, you'll
ignore it?

> +	spin_lock_irqsave(&fgd->lock, flags);
> +	fgd->bulk_pending = true;
> +	spin_unlock_irqrestore(&fgd->lock, flags);
> +
> +	queue_work(system_long_wq, &fgd->worker);

Do you need to offset this to a worker?

> +static int f_gud_drm_ctrl_req_set_buffer(struct f_gud_drm *fgd, void *buf, size_t len)
> +{
> +	int ret;
> +
> +	if (len != sizeof(struct gud_drm_req_set_buffer))
> +		return -EINVAL;
> +
> +	ret = gud_drm_gadget_set_buffer(fgd->gdg, buf);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (ret > fgd->max_buffer_size)
> +		return -EOVERFLOW;
> +
> +	fgd->bulk_req->length = ret;
> +
> +	return usb_ep_queue(fgd->bulk_ep, fgd->bulk_req, GFP_KERNEL);
> +}
> +
> +static void f_gud_drm_worker(struct work_struct *work)
> +{
> +	struct f_gud_drm *fgd = container_of(work, struct f_gud_drm, worker);
> +	bool ctrl_pending, bulk_pending, disable_pending;
> +	struct gud_drm_gadget *gdg = fgd->gdg;
> +	unsigned long flags;
> +	u16 request, value;
> +	int ret;
> +
> +	spin_lock_irqsave(&fgd->lock, flags);
> +	request = fgd->request;
> +	value = fgd->value;
> +	ctrl_pending = fgd->ctrl_pending;
> +	bulk_pending = fgd->bulk_pending;
> +	disable_pending = fgd->disable_pending;
> +	spin_unlock_irqrestore(&fgd->lock, flags);
> +
> +	pr_debug("%s: bulk_pending=%u ctrl_pending=%u disable_pending=%u\n",
> +		 __func__, bulk_pending, ctrl_pending, disable_pending);

could we use dev_dbg() at least?

-- 
balbi

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