Messages in this thread | | | Date | Thu, 11 Sep 2014 09:37:38 +0800 | From | Robin Gong <> | Subject | Re: [PATCH v5] spi: spi-imx: add DMA support |
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On Wed, Sep 10, 2014 at 04:52:16PM +0100, Mark Brown wrote: > 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. Understood, will improve it in v6.Thanks.
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