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Date:   Thu, 28 Apr 2022 14:15:22 +0900
From:   Jung Daehwan <dh10.jung@samsung.com>
To:     Mathias Nyman <mathias.nyman@linux.intel.com>
Cc:     Mathias Nyman <mathias.nyman@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "open list:USB XHCI DRIVER" <linux-usb@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        Howard Yen <howardyen@google.com>,
        Jack Pham <jackp@codeaurora.org>,
        Puma Hsu <pumahsu@google.com>,
        "J . Avila" <elavila@google.com>, sc.suh@samsung.com,
        Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Subject: Re: [PATCH v4 5/5] usb: host: add xhci-exynos driver
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On Wed, Apr 27, 2022 at 07:25:21PM +0300, Mathias Nyman wrote:
> 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@samsung.com>
> 
> 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.  
> 
> (...)
> 

I missed replying here on previous one.
OK. It seems to need more detailed explanation. I will explain my driver
more detail on next submission.

> > +
> > +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.
> 
> 

I missed it also on previous mail.
I've never seen a device that has several isoc endpoints.
It needs to add something if it would exist.

In fact, I've found a device that has feedback ep and I'm going to add
it. I've never seen other case yet.

Best Regards,
Jung Daehwan

> > +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
> 

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