On Mon, Jun 08, 2020 at 03:08:45PM +0000, Robin Gong wrote:
> > > + if (transfer->rx_sg.sgl) {
> > > + struct device *rx_dev = spi->controller->dma_rx->device->dev;
> > > +
> > > + dma_sync_sg_for_device(rx_dev, transfer->rx_sg.sgl,
> > > + transfer->rx_sg.nents, DMA_TO_DEVICE);
> > > + }
> > > +> > This is confusing - why are we DMA mapping to the device after doing a PIO > > transfer? > 'transfer->rx_sg.sgl' condition check that's the case fallback PIO after DMA > transfer > failed. But the spi core still think the buffer should be in 'device' while > spi driver > touch it by PIO(CPU), so sync it back to device to ensure all received data > flush to DDR. So we sync it back to the device so that we can then do another sync to CPU? TBH I'm a bit surprised that there's a requirement that we explicitly undo a sync and that a redundant double sync in the same direction might be an issue but I've not had a need to care so I'm perfectly prepared to believe there is. At the very least this needs a comment.
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