Re: [PATCH v4 5/5] usb: host: add xhci-exynos driver

[Mathias Nyman]

On 26.4.2022 12.18, Daehwan Jung wrote:
> This driver is for Samsung Exynos xhci host conroller. It uses xhci-plat
> driver mainly and extends some functions by xhci hooks and overrides.
> 
> It supports USB Audio offload with Co-processor. It only cares DCBAA,
> Device Context, Transfer Ring, Event Ring, and ERST. They are allocated
> on specific address with xhci hooks. Co-processor could use them directly
> without xhci driver after then.
> 
> Signed-off-by: Daehwan Jung <dh10.jung@xxxxxxxxxxx>

I have to agree with Krzysztof's comments, this is an odd driver stub.

Perhaps open up a bit how the Exynos offloading works so we can figure out
in more detail what the hardware needs from software.  

(...)

> +
> +static void xhci_exynos_alloc_container_ctx(struct xhci_hcd *xhci, struct xhci_container_ctx *ctx,
> +						int type, gfp_t flags)
> +{
> +	/* Only first Device Context uses URAM */
> +	int i;
> +
> +	ctx->bytes = ioremap(EXYNOS_URAM_DEVICE_CTX_ADDR, EXYNOS_URAM_CTX_SIZE);
> +	if (!ctx->bytes)
> +		return;
> +
> +	for (i = 0; i < EXYNOS_URAM_CTX_SIZE; i++)
> +		ctx->bytes[i] = 0;
> +
> +	ctx->dma = EXYNOS_URAM_DEVICE_CTX_ADDR;

This can't work with more than one USB device.
This hardcodes the same context address for every usb device.


> +static void xhci_exynos_parse_endpoint(struct xhci_hcd *xhci, struct usb_device *udev,
> +		struct usb_endpoint_descriptor *desc, struct xhci_container_ctx *ctx)
> +{
> +	struct xhci_plat_priv *priv = xhci_to_priv(xhci);
> +	struct xhci_hcd_exynos *xhci_exynos = priv->vendor_priv;
> +	struct usb_endpoint_descriptor *d = desc;
> +	unsigned int ep_index;
> +	struct xhci_ep_ctx *ep_ctx;
> +
> +	ep_index = xhci_get_endpoint_index(d);
> +	ep_ctx = xhci_get_ep_ctx(xhci, ctx, ep_index);
> +
> +	if ((d->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK) ==
> +				USB_ENDPOINT_XFER_ISOC) {
> +		if (d->bEndpointAddress & USB_ENDPOINT_DIR_MASK)
> +			xhci_exynos->in_ep = d->bEndpointAddress;
> +		else
> +			xhci_exynos->out_ep = d->bEndpointAddress;
> +	}

This won't work if more than one device that has isoc endpoints, or even 
if that device has more than one in/out isoc endpoint pair.


> +static int xhci_alloc_segments_for_ring_uram(struct xhci_hcd *xhci,
> +		struct xhci_segment **first, struct xhci_segment **last,
> +		unsigned int num_segs, unsigned int cycle_state,
> +		enum xhci_ring_type type, unsigned int max_packet, gfp_t flags,
> +		u32 endpoint_type)
> +{
> +	struct xhci_segment *prev;
> +	bool chain_links = false;
> +
> +	while (num_segs > 0) {
> +		struct xhci_segment *next = NULL;
> +
> +		if (!next) {
> +			prev = *first;
> +			while (prev) {
> +				next = prev->next;
> +				xhci_segment_free(xhci, prev);
> +				prev = next;
> +			}
> +			return -ENOMEM;

This always return -ENOMEM

Also this whole function never allocates or remaps any memory.

> +		}
> +		xhci_link_segments(prev, next, type, chain_links);
> +
> +		prev = next;
> +		num_segs--;
> +	}
> +	xhci_link_segments(prev, *first, type, chain_links);
> +	*last = prev;
> +
> +	return 0;
> +}
> +
> +static struct xhci_ring *xhci_ring_alloc_uram(struct xhci_hcd *xhci,
> +		unsigned int num_segs, unsigned int cycle_state,
> +		enum xhci_ring_type type, unsigned int max_packet, gfp_t flags,
> +		u32 endpoint_type)
> +{
> +	struct xhci_ring	*ring;
> +	int ret;
> +	struct device *dev = xhci_to_hcd(xhci)->self.sysdev;
> +
> +	ring = kzalloc_node(sizeof(*ring), flags, dev_to_node(dev));
> +	if (!ring)
> +		return NULL;
> +
> +	ring->num_segs = num_segs;
> +	ring->bounce_buf_len = max_packet;
> +	INIT_LIST_HEAD(&ring->td_list);
> +	ring->type = type;
> +	if (num_segs == 0)
> +		return ring;
> +
> +	ret = xhci_alloc_segments_for_ring_uram(xhci, &ring->first_seg,
> +			&ring->last_seg, num_segs, cycle_state, type,
> +			max_packet, flags, endpoint_type);
> +	if (ret)
> +		goto fail;
> +
> +	/* Only event ring does not use link TRB */
> +	if (type != TYPE_EVENT) {
> +		/* See section 4.9.2.1 and 6.4.4.1 */
> +		ring->last_seg->trbs[TRBS_PER_SEGMENT - 1].link.control |=
> +			cpu_to_le32(LINK_TOGGLE);

No memory was allocated for trbs

A lot of this code seems to exists just to avoid xhci driver from allocating
dma capable memory, we can refactor the existing xhci_mem_init() and move
dcbaa and event ring allocation and other code to their own overridable
functions.

This way we can probably get rid of a lot of the code in this series.

Thanks
Mathias