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

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Message-ID: <20130412161325.GB18459@gmail.com>
Date:	Fri, 12 Apr 2013 17:13:25 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Rabin Vincent <rabin@....in>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	arnd@...db.de, linus.walleij@...ricsson.com
Subject: Re: [PATCH 3/8] dmaengine: ste_dma40: Actually write the runtime
 configuration to registers

On Fri, 12 Apr 2013, Rabin Vincent wrote:

> 2013/4/9 Lee Jones <lee.jones@...aro.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().

Ah, I see. I'll move it all back and investigate my bug further then.

Thanks for taking the time to write such a well written review.

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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