Re: [PATCH] mmc: dw_mmc: modified the DMA threshold for SD card

[Jaehoon Chung <jh80.chung@samsung.com>]

James Hogan wrote:

> On 09/22/2011 11:01 AM, Jaehoon Chung wrote:
>> This patch modified the DMA threshold.
>>
>> I didn't know exactly why need this threshold.
>> But if this value is 16, we didn't read SCR register for SD card.
>> Because in mmc_app_send_scr this values are used data.blocks=1 and data.blksz=8.
>> (data.blocks * data.blksz = 8...so return -EINVAL)
> 
> The idea is that for a small transaction the time to set up the DMA is
> probably not worth the effort, therefore it does it using PIO mode (see
> dw_mci_submit_data, if dw_mci_submit_data_dma fails, it sets itself up
> for pio mode instead).

Is there some reason that threshold is set 16?

> 
> So if it's using PIO mode and the SCR cannot be read, then PIO mode is
> broken. What's the value of the register HCON? dw_mci_probe reads it and
> decides which pio push and pull function to use based on the host data
> width. I've only tested one of them as we only have one configuration of
> hardware available, but you may have a different one.


i used push/pull_data_32. What do you doubt this problem?

Best regards,
Jaehon Chung