Re: [PATCH] musb: fix ISOC Tx programming for CPPI DMAs

[Sergei Shtylyov <sshtylyov-hkdhdckH98+B+jHODAdFcQ@public.gmane.org>]

Hello, I wrote:

>>>>> This part is being done at musb_host_rx()

>>>>   You're doing it in musb_host_tx() actually. Although musb_host_rx()
>>>> is also broken WRT the isochronous transfers.

>>>>> doing next packet programming within same urb and *not* starting next

>>>> urb. Thus musb_start_urb() doesn't come into this path.

>>>>   What? Read the code, please -- musb_start_urb() call should always
>>>> precede musb_host_tx() which handles the DMA interrupt. Unless 
>>>> something
>>>> clears DMAReqEnab after musb_start_urb() call, setting it only once
>>>> should work.

>>> musb_start_urb() call does precede musb_host_tx() but when urb is
>>> *completed*.

>> I think you are aware that there are multiple packets within same 
>> isochronous urb and musb_start_urb() programs only for first packet.

>> ============================================================
>>         case USB_ENDPOINT_XFER_ISOC:
>>                 qh->iso_idx = 0;
>>                 qh->frame = 0;
>>                 offset = urb->iso_frame_desc[0].offset;
>>                 len = urb->iso_frame_desc[0].length;
>> ============================================================

>    Sure. What I'm still not aware of is where and how the TXCSR DMA bits 
> are cleared after the first fragment. Hopefully, testing will reveal 
> this...

    I really should have stared at the code a bit more myself. Now that I 
have the sad truth has dawned on me... :-/
    My patch "USB: musb: bugfixes for multi-packet TXDMA support" (commit 
c7bbc056a92476b3b3d70a8df7cc746ac5d56de7) inevitably causes the DMA bits to 
be cleared because we're using DMA mode 1 regardless of whether this is 
isochronous transfer or no.  (We could really use mode 0 for isochronous 
transfer and save the hassle when filtering out DMA completion interrupt in 
musb_host_tx().)
    So, I now have to ACK your patch (which could use a better description 
though) and strew my head with ashes. All this also must mean that I have 
managed to break ISO Tx DMA in the internal tree, where I added the 
abovementioned patch after the one that fixed it (the order of the patches 
in the community tree is reverse). I probably did not retest USB audio back 
then...

WBR, Sergei

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