Re: [PATCH] dma: add new DMA control commands

[Huang Shijie <b32955@freescale.com>]

于 2012年10月18日 15:14, Marek Vasut 写道:
> Dear Huang Shijie,
>
> Why such massive CC ?
>
>> 于 2012年10月18日 14:18, Vinod Koul 写道:
>>> Why cant you do start (prepare clock etc) when you submit the descriptor
>>> to dmaengine. Can be done in tx_submit callback.
>>> Similarly remove the clock when dma transaction gets completed.
>> I ever thought this method too.
>>
>> But it will become low efficient in the following case:
>>
>>     Assuming the gpmi-nand driver has to read out 1024 pages in one
>> _SINGLE_ read operation.
>> The gpmi-nand will submit the descriptor to dmaengine per page.
> It will? Then GPMI NAND is flat our broken ... again.
yes.

Please read the NAND chip spec about the comand READ PAGE(00h-30h) and 
the code
nand_do_read_ops(). The nand chip limits us only read one page out one time.
So the driver will submit the descriptor to dmaengine per page.



>> So with
>> your method,
>> the system will repeat the enable/disable dma clock 1024 time.
> Yes, it is the driver that's wrong.
not the driver.
>> At every
>> enable/disable dma clock,
>> the system has to enable the clock chain and it's parents ...
>>
>> But with this patch, we only need to enable/disable dma clock one time,
>> just at we select the nand chip.
> You are fixing a driver problem at a framework level, wrong.
>
> So, check how the MXS SPI driver handles descriptor chaining. Indeed, the
> Sigmatel screwed the DMA stuff good. But if you analyze the SPI driver, you'll
> notice a few important points that might come handy when you fix the GPMI NAND
> driver properly.
>
> The direction to take here is:
> 1) Implement DMA chaining into the GPMI NAND driver
How can i implement the DMA chain if the nand chip READ-PAGE command 
gives us the one page limit?

thanks
Huang Shijie


> 2) You might need to do one PIO transfer to reconfigure the IP registers between
> each segment of the DMA chain (just as MXS SPI does it)
> 3) You might run out of DMA descriptors when doing too long chains -- so you
> might need to fix that part of the mxs DMA driver.