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SubjectRe: [PATCH v2 1/2] usb: dwc2: alloc dma aligned buffer for isoc split in
From
Date
Dear Doug,


在 2018年05月02日 12:33, Doug Anderson 写道:
> Hi,
>
> On Tue, May 1, 2018 at 8:04 PM, William Wu <william.wu@rock-chips.com> wrote:
>> The commit 3bc04e28a030 ("usb: dwc2: host: Get aligned DMA in
>> a more supported way") rips out a lot of code to simply the
>> allocation of aligned DMA. However, it also introduces a new
>> issue when use isoc split in transfer.
>>
>> In my test case, I connect the dwc2 controller with an usb hs
>> Hub (GL852G-12), and plug an usb fs audio device (Plantronics
>> headset) into the downstream port of Hub. Then use the usb mic
>> to record, we can find noise when playback.
>>
>> It's because that the usb Hub uses an MDATA for the first
>> transaction and a DATA0 for the second transaction for the isoc
>> split in transaction. An typical isoc split in transaction sequence
>> like this:
>>
>> - SSPLIT IN transaction
>> - CSPLIT IN transaction
>> - MDATA packet
>> - CSPLIT IN transaction
>> - DATA0 packet
>>
>> The DMA address of MDATA (urb->dma) is always DWORD-aligned, but
>> the DMA address of DATA0 (urb->dma + qtd->isoc_split_offset) may
>> not be DWORD-aligned, it depends on the qtd->isoc_split_offset (the
>> length of MDATA). In my test case, the length of MDATA is usually
>> unaligned, this casue DATA0 packet transmission error.
>>
>> This patch base on the old way of aligned DMA allocation in the
>> dwc2 driver to get aligned DMA for isoc split in.
>>
>> Signed-off-by: William Wu <william.wu@rock-chips.com>
>> ---
>> Changes in v2:
>> - None
>>
>> drivers/usb/dwc2/hcd.c | 63 +++++++++++++++++++++++++++++++++++++++++---
>> drivers/usb/dwc2/hcd.h | 10 +++++++
>> drivers/usb/dwc2/hcd_intr.c | 8 ++++++
>> drivers/usb/dwc2/hcd_queue.c | 8 +++++-
>> 4 files changed, 85 insertions(+), 4 deletions(-)
> A word of warning that I'm pretty rusty on dwc2 and even when I was
> making lots of patches I still considered myself a bit clueless.
> ...so if something seems wrong, please call me on it...
Most of your suggestions are great, thanks very much!
>
>> diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
>> index 190f959..8c2b35f 100644
>> --- a/drivers/usb/dwc2/hcd.c
>> +++ b/drivers/usb/dwc2/hcd.c
>> @@ -1562,11 +1562,20 @@ static void dwc2_hc_start_transfer(struct dwc2_hsotg *hsotg,
>> }
>>
>> if (hsotg->params.host_dma) {
>> - dwc2_writel((u32)chan->xfer_dma,
>> - hsotg->regs + HCDMA(chan->hc_num));
>> + dma_addr_t dma_addr;
>> +
>> + if (chan->align_buf) {
>> + if (dbg_hc(chan))
>> + dev_vdbg(hsotg->dev, "align_buf\n");
>> + dma_addr = chan->align_buf;
>> + } else {
>> + dma_addr = chan->xfer_dma;
>> + }
>> + dwc2_writel((u32)dma_addr, hsotg->regs + HCDMA(chan->hc_num));
>> +
>> if (dbg_hc(chan))
>> dev_vdbg(hsotg->dev, "Wrote %08lx to HCDMA(%d)\n",
>> - (unsigned long)chan->xfer_dma, chan->hc_num);
>> + (unsigned long)dma_addr, chan->hc_num);
>> }
>>
>> /* Start the split */
>> @@ -2620,6 +2629,33 @@ static void dwc2_hc_init_xfer(struct dwc2_hsotg *hsotg,
>> }
>> }
>>
>> +static int dwc2_alloc_split_dma_aligned_buf(struct dwc2_hsotg *hsotg,
>> + struct dwc2_qh *qh,
>> + struct dwc2_host_chan *chan)
>> +{
>> + if (!qh->dw_align_buf) {
>> + qh->dw_align_buf = kmalloc(chan->max_packet,
> So you're potentially doing a bounce buffer atop a bounce buffer now,
> right? That seems pretty non-optimal. You're also back to doing a
> kmalloc at interrupt time which I found was pretty bad for
> performance.
Yes, I just allocate an additional bounce buffer here. I haven't thought
consummately
about this patch, it's really not a good way to use a kmalloc at
interrut time.
> Is there really no way you can do your memory allocation in
> dwc2_alloc_dma_aligned_buffer() instead of here? For input packets,
> if you could just allocate an extra 3 bytes in the original bounce
> buffer you could just re-use the original bounce buffer together with
> a memmove? AKA:
>
> transfersize = 13 + 64;
> buf = alloc(16 + 64);
>
> // Do the first transfer, no problems.
> dma_into(buf, 13);
>
> // 2nd transfer isn't aligned, so align.
> // we allocated a little extra to account for this
> dma_into(buf + 16, 64);
>
> // move back where it belongs.
> memmove(buf + 13, buf + 16, 64);
>
>
> To make the above work you'd need to still allocate a bounce buffer
> even if the original "urb->transfer_buffer" was already aligned.
> Ideally you'd be able to know when dwc2_alloc_dma_aligned_buffer()
> that this is one of the special cases where you need a slightly
> oversized bounce buffer.
It's a good way to allocate an extra 3 bytes in the original bounce
buffer for this unaligned
issue, it's similar to the tailroom of sk_buff. However, just as you
said, we'd better find
the special cases where we need an oversized bounce buffer, otherwise,we
need to allocate
a bounce buffer for all of urbs.

It's hard for me to know the special cases in the
dwc2_alloc_dma_aligned_buffer(), because
it's called from usb_submit_urb() in the device class driver, and I
hardly know the split state
in this process, much less if the split transaction need aligned buffer.
Do you have any idea?

I suppose that we can't find the special cases where we need an
oversized bounce buffer
in the dwc2_alloc_dma_aligned_buffer(), and if we still want to re-use
the original bounce
buffer with extra 3 bytes, then we need to allocate a  bounce buffer for
all of urbs, and do
unnecessary  data copy for these urbs  whose transfer_buffer were
already aligned.  This
may reduce the transmission rate of USB.

Can we just pre-allocate an additional aligned buffer (the size is 200
bytes) for split transaction
in dwc2_map_urb_for_dma for all of urbs. And if we find the split
transaction is unaligned,
we can easily use the pre-allocated aligned buffer.
>
> ---
>
> If you somehow need to do something for output, you'd do the opposite.
> You'd copy backwards top already transferred data to align.
>
>
>> + GFP_ATOMIC | GFP_DMA);
>> + if (!qh->dw_align_buf)
>> + return -ENOMEM;
>> +
>> + qh->dw_align_buf_size = chan->max_packet;
>> + }
>> +
>> + qh->dw_align_buf_dma = dma_map_single(hsotg->dev, qh->dw_align_buf,
>> + qh->dw_align_buf_size,
>> + DMA_FROM_DEVICE);
>> +
>> + if (dma_mapping_error(hsotg->dev, qh->dw_align_buf_dma)) {
>> + dev_err(hsotg->dev, "can't map align_buf\n");
>> + chan->align_buf = 0;
>> + return -EINVAL;
>> + }
>> +
>> + chan->align_buf = qh->dw_align_buf_dma;
>> + return 0;
>> +}
>> +
>> #define DWC2_USB_DMA_ALIGN 4
>>
>> struct dma_aligned_buffer {
>> @@ -2797,6 +2833,27 @@ static int dwc2_assign_and_init_hc(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
>> /* Set the transfer attributes */
>> dwc2_hc_init_xfer(hsotg, chan, qtd);
>>
>> + /* For non-dword aligned buffers */
>> + if (hsotg->params.host_dma > 0 && qh->do_split &&
>> + chan->ep_is_in && (chan->xfer_dma & 0x3)) {
> So what happens if were unaligned (AKA (chan->xfer_dma & 0x3)) but
> we're not doing split or it's not an IN EP? Do we just fail then?
>
> I guess the rest of this patch only handles the "in" case and maybe
> you expect that the problems will only come about for do_split, but it
> still might be wise to at least print a warning in the other cases?
> >From reading dwc2_hc_init_xfer() it seems like you could run into this
> same problem in the "out" case?
Actually, I only find non-dword aligned issue in the case of split in
transaction.
And I think that if we're not doing split or it's an OUT EP, we can
always get aligned buffer
in the current code. For non-split case, the
dwc2_alloc_dma_aligned_buffer()
is enough. And for split out case, if the transaction is subdivided into
multiple start-splits,
each with a data payload of 188 bytes or less, so the DMA address is
always aligned.

>
>
>> + dev_vdbg(hsotg->dev, "Non-aligned buffer\n");
>> + if (dwc2_alloc_split_dma_aligned_buf(hsotg, qh, chan)) {
>> + dev_err(hsotg->dev,
>> + "%s: Failed to allocate memory to handle non-dword aligned buffer\n",
>> + __func__);
> Here and elsewhere in this patch: In general I think policy is that
> you shouldn't include __func__ for dev_err(). The string together
> with the name of the device is supposed to uniquely determine where
> you are.
Ah, I got it. I will fix it in next patch.
>> + /* Add channel back to free list */
>> + chan->align_buf = 0;
>> + chan->multi_count = 0;
>> + list_add_tail(&chan->hc_list_entry,
>> + &hsotg->free_hc_list);
>> + qtd->in_process = 0;
>> + qh->channel = NULL;
>> + return -ENOMEM;
>> + }
>> + } else {
>> + chan->align_buf = 0;
>> + }
>> +
>> if (chan->ep_type == USB_ENDPOINT_XFER_INT ||
>> chan->ep_type == USB_ENDPOINT_XFER_ISOC)
>> /*
>> diff --git a/drivers/usb/dwc2/hcd.h b/drivers/usb/dwc2/hcd.h
>> index 96a9da5..adf1fd0 100644
>> --- a/drivers/usb/dwc2/hcd.h
>> +++ b/drivers/usb/dwc2/hcd.h
>> @@ -76,6 +76,8 @@ struct dwc2_qh;
>> * (micro)frame
>> * @xfer_buf: Pointer to current transfer buffer position
>> * @xfer_dma: DMA address of xfer_buf
>> + * @align_buf: In Buffer DMA mode this will be used if xfer_buf is not
>> + * DWORD aligned
> Your patch uses tabs but everything else in this comment uses spaces.
> Please be consistent with surrounding code. It looks like I may have
> screwed this up in the past on the comment of "struct dwc2_qh", but
> that's no reason to mess it up again...
Ah, I got it. I will fix it in next patch.
>
>> * @xfer_len: Total number of bytes to transfer
>> * @xfer_count: Number of bytes transferred so far
>> * @start_pkt_count: Packet count at start of transfer
>> @@ -133,6 +135,7 @@ struct dwc2_host_chan {
>>
>> u8 *xfer_buf;
>> dma_addr_t xfer_dma;
>> + dma_addr_t align_buf;
>> u32 xfer_len;
>> u32 xfer_count;
>> u16 start_pkt_count;
>> @@ -303,6 +306,10 @@ struct dwc2_hs_transfer_time {
>> * is tightly packed.
>> * @ls_duration_us: Duration on the low speed bus schedule.
>> * @ntd: Actual number of transfer descriptors in a list
>> + * @dw_align_buf: Used instead of original buffer if its physical address
>> + * is not dword-aligned
>> + * @dw_align_buf_size: Size of dw_align_buf
>> + * @dw_align_buf_dma: DMA address for dw_align_buf
>> * @qtd_list: List of QTDs for this QH
>> * @channel: Host channel currently processing transfers for this QH
>> * @qh_list_entry: Entry for QH in either the periodic or non-periodic
>> @@ -350,6 +357,9 @@ struct dwc2_qh {
>> struct dwc2_hs_transfer_time hs_transfers[DWC2_HS_SCHEDULE_UFRAMES];
>> u32 ls_start_schedule_slice;
>> u16 ntd;
>> + u8 *dw_align_buf;
>> + int dw_align_buf_size;
>> + dma_addr_t dw_align_buf_dma;
>> struct list_head qtd_list;
>> struct dwc2_host_chan *channel;
>> struct list_head qh_list_entry;
>> diff --git a/drivers/usb/dwc2/hcd_intr.c b/drivers/usb/dwc2/hcd_intr.c
>> index a5dfd9d..5e2378f 100644
>> --- a/drivers/usb/dwc2/hcd_intr.c
>> +++ b/drivers/usb/dwc2/hcd_intr.c
>> @@ -938,6 +938,14 @@ static int dwc2_xfercomp_isoc_split_in(struct dwc2_hsotg *hsotg,
>>
>> frame_desc->actual_length += len;
>>
>> + if (chan->align_buf) {
>> + dev_vdbg(hsotg->dev, "%s(): non-aligned buffer\n", __func__);
>> + dma_unmap_single(hsotg->dev, chan->qh->dw_align_buf_dma,
>> + chan->qh->dw_align_buf_size, DMA_FROM_DEVICE);
>> + memcpy(qtd->urb->buf + frame_desc->offset +
>> + qtd->isoc_split_offset, chan->qh->dw_align_buf, len);
> Assuming I'm understanding this patch correctly, I think it would be
> better to write:
>
> memcpy(qtd->xfer_dma, chan->qh->dw_align_buf, len);
Sorry, there's no "xfer_buf" in qtd, do you means the "chan->xfer_dma"?
If it's, I think we can't
do memcpy from a transfer buffer to a DMA address. Maybe chan->xfer_buf
is more suitable,
but it seems that the dwc2 driver doesn't update the chan->xfer_buf for
isoc transfer with dma
enabled in dwc2_hc_init_xfer().
>
> Then if you ever end up having to align a transfer other than a split
> you won't be doing the wrong math. As it is it's very non-obvious
> that you're hardcoding the same formula that's in dwc2_hc_init_xfer()
Actually, I'm hardcoding the same formula from the old code which has
been ripped out
in the commit 3bc04e28a030 ("usb: dwc2: host: Get aligned DMA in a more
supported way").
>
>
>> + }
>> +
>> qtd->isoc_split_offset += len;
>>
>> hctsiz = dwc2_readl(hsotg->regs + HCTSIZ(chnum));
>> diff --git a/drivers/usb/dwc2/hcd_queue.c b/drivers/usb/dwc2/hcd_queue.c
>> index e34ad5e..a120bb0 100644
>> --- a/drivers/usb/dwc2/hcd_queue.c
>> +++ b/drivers/usb/dwc2/hcd_queue.c
>> @@ -1693,8 +1693,14 @@ void dwc2_hcd_qh_free(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
>>
>> dwc2_host_put_tt_info(hsotg, qh->dwc_tt);
>>
>> - if (qh->desc_list)
>> + if (qh->desc_list) {
>> dwc2_hcd_qh_free_ddma(hsotg, qh);
>> + } else {
>> + /* kfree(NULL) is safe */
>> + kfree(qh->dw_align_buf);
>> + qh->dw_align_buf_dma = (dma_addr_t)0;
> Why assign qh->dw_align_buf_dma to 0? The next thing you're doing is
> kfree(qh). If you want extra debugging, turn on slub_debug.
I just copy the same code from the old code which has been ripped out in the
commit 3bc04e28a030 ("usb: dwc2: host: Get aligned DMA in a more
supported way").
I really don't know why assign qh->dw_align_buf_dma to 0.
>
>
>> + }
>> +
>> kfree(qh);
>> }
>
>


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