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

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Date:   Tue, 3 May 2022 17:41:58 +0900
From:   Jung Daehwan <dh10.jung@...sung.com>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Howard Yen <howardyen@...gle.com>,
        Jack Pham <jackp@...eaurora.org>,
        Puma Hsu <pumahsu@...gle.com>,
        "J . Avila" <elavila@...gle.com>, sc.suh@...sung.com,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Subject: Re: [PATCH v4 5/5] usb: host: add xhci-exynos driver

On Thu, Apr 28, 2022 at 03:28:49PM +0300, Mathias Nyman wrote:
> On 28.4.2022 6.03, Jung Daehwan wrote:
> > 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@...sung.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.  
> >>
> >> (...)
> > 
> >>> +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
> > 
> > Yes. it's right to return error here.
> > 
> 
> Still don't think that is the case.
> 
> So if the num_segs value passed to a function named
> xhci_alloc_segments_for_ring_uram() is anything else than 0, it will 
> automatically return -ENOMEM?
> 
> >>
> >> Also this whole function never allocates or remaps any memory.
> > 
> > This fuctions is for link segments. Right below function(xhci_ring_alloc_uram)
> > allocates.
> 
> Still doesn't allocate any ring segments.
> Below function only allocates memory for the
> ring structure that contains pointers to segments.
> 

When I re-check it, it has a problem as you said.
I will modify it on next submission. Thanks.

Best Regards,
Jung Daehwan

> > 
> >>
> >>> +		}
> >>> +		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
> > 
> > Allcation function for trbs are missed. It's done by ioremap.
> > I will add it on next submission. Thanks for the comment.
> > 
> >>
> >> 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.
> > 
> > Yes right. I think it's proper. Do you agree with it or have better way
> > to do it?
> 
> Could be, but I don't have a good picture of how this Exynos audio offloading
> works, so it's hard to guess.
> 
> Thanks
> -Mathias
>