On Wed, Sep 10, 2014 at 11:18:01PM +0800, Robin Gong wrote: > On Wed, Sep 10, 2014 at 12:45:30PM +0100, Mark Brown wrote: > > > Yes, you're right. I should use "transfer->tx_sg->sgl == NULL" or > > > "transfer->rx_sg->sgl == NULL" instead of usedma flag in driver, right? > > Right. > But looks spi core framework can make sure every rx or tx transfer in sequence. > If so, can_dma will never be called until this transfer finished > (spi_pump_messages), and my usedma flag also never be modified until next > transfer start. Please correct me if I am wrong, thanks. Even if that were true currently this would still not be good code since it would break in the face of SPI core changes. In any case the assumption isn't true for the current SPI core, the DMA mapping is done for all transfers in a message before we start running them and it's entirely likely that we will have patterns like a short PIO transfer followed by a big data block.
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