[PATCH 3/8] dmaengine: ste_dma40: Actually write the runtime configuration to registers

[Rabin Vincent]

2013/4/15 Lee Jones <lee.jones at linaro.org>:
> On Fri, 12 Apr 2013, Rabin Vincent wrote:
>> 2013/4/9 Lee Jones <lee.jones at linaro.org>:
>> > Someone has spent a fair amount of effort writing a runtime configuration
>> > changing algorithm for DMA clients. However, the config appears to never
>> > actually make it to hardware. In order for the configuration to take hold
>> > we need to issue a d40_config_write(), as this is the routine which writes
>> > it into the hardware's registers.
>>
>> No, it's not.  This function is only for initial configuration which
>> should only be written when the channel is allocated.  In fact, by
>> calling it here in runtime_config, you are introducing a serious bug:
>> other logical channels on the same physical channel will stop because of
>> the SSLNK/SDLNK of the physical channel being zeroed.
>>
>> The runtime config already makes it the hardware in the existing code,
>> via d40_*_cfg().
>
> Sorry Rabin, but the only place I can see the config being written is
> in d40_config_write().
>
> Can you paste the line of code in d40_*_cfg() which actually writes
> the config to hardware please? I don't see it.

It's not that simple.  There are some pointers passed to d40_*_cfg() and
that function writes the configuration to the variables those pointers
point to (d40c->log_def.lcsp1, d40c->src_def_cfg, etc.).  Please read
the code to see how those variables end up being used later when the
LLIs are prepared for the HW.