a bulk urb with both PIO and DMA buffer?
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- To: linux-usb@xxxxxxxxxxxxxxx
- Subject: a bulk urb with both PIO and DMA buffer?
- From: Randy Li <ayaka@xxxxxxxxxxx>
- Date: Tue, 10 Oct 2023 05:53:38 +0800
- Cc: linux-spi@xxxxxxxxxxxxxxx
- User-agent: Mozilla Thunderbird
Hello
I am trying to write a driver for a USB-SPI adapter(WCH347). The
protocol of this chip would be consist with two parts, operate code and
payload length would be the first part. SPI framework could prepare the
sg_table for the second part which is the payload.
It is worth to do dma transfer for the second part of a bulk packet, but
I have to prepend a small buffer before it. Then I have to copy the
scatterlist from the sg_table to append to a new scatter list, that
costs CPU a lot.
I wonder if there is a way that I could construct a bulk packet with two
URBs or anyway to make the URB first try a bytes of PIO then DMA?
Sincerely
Randy
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