Re: [PATCH] OMAP: McSPI: Fix RX DMA transfer path

[Aaro Koskinen <aaro.koskinen@nokia.com>]

Hello,

ext Hemanth V wrote:
> From: "Aaro Koskinen" <aaro.koskinen@nokia.com>
>> From: Eero Nurkkala <ext-eero.nurkkala@nokia.com>
>>
>> When data is read through DMA, the last element must be read separately
>> through the RX register. It cannot be transferred by the DMA. For further
>> details see e.g. OMAP3430 TRM.
> 
> Could you provide the section number and the version of TRM you are
> referring to.

Table 19-16 and section 19.6.2.5.1 in the public TRM.

>> Without the fix the driver causes extra clocks to be clocked to the
>> bus after DMA RX operations. This can cause interesting behaviour with
>> some devices.
> 
> Could you provide more details on the errors seen i.e is the transfer 
> aborted

There is an extra word, which a device can interpret as a command. Also 
if the word size != command size the device can hang. Unless the device 
hangs, you may not even notice anything.

A.