Ming Lei wrote:
Hi All,
In another thread, Sergei pointed out there is a ZLP issue in musb_g_tx:
Sergei Shtylyov <sshtylyov@xxxxxxxxxx> wrote:
Hello.
On 15-09-2010 14:05, Felipe Balbi wrote:
I didn't say it was duplicate for DMA, just too late.
how come ? we need to send ZLP before giving back the request.
Well, look at the code ionce again. We need to send ZLP *after*
request->actual == request->length, but as the check is inserted
after the ZLP send, ZLP *may* be sent once the first DMA completes,
not the last.
WBR, Sergei
balbi also confirmed that is is really a problem.
I also have two related questions below for the problem:
1), why is the check for "is_dma" needed here?
if (is_dma || request->actual == request->length) {
....
}
I'm not sure -- it seems erratic.
2), why is a zlp needed in the case below?
#ifdef CONFIG_USB_INVENTRA_DMA
|| (is_dma && (!dma->desired_mode ||
(request->actual & (musb_ep->packet_sz - 1))))
#endif
Seems no request->zero is set to ask for zlp explicitly in
the case above.
This is not for ZLP -- this is here to set TXPktRdy for the last short
packet in the Inventra DMA mode 0 that doesn't set TXPktRdy in such case.
IMO, it is not difficult to give a good fix for the ZLP problem
if the two questions are clear.
WBR, Sergei
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