Re: [PATCH] dma: tegra: enable/disable dma clock

From: Laxman Dewangan
Date: Fri Jul 20 2012 - 02:13:25 EST

On Friday 20 July 2012 11:32 AM, Vinod Koul wrote:
On Wed, 2012-07-18 at 14:26 +0530, Laxman Dewangan wrote:
Enable the DMA clock when registering DMA driver and
disable clock when removing the DMA driver.

The failure was observed on Tegra20 based system by
Stephen Warren. However, it is working fine on tegra30
based system and probably becasue uboot enable the clock
on Tegra30.
Don't know much about the clock subsystem, but shouldn't the clocks be
enabled runtime..... when you actually start using the controller??

Yes, this is the plan and I am going to implement dynamic clock management but it will take some time to complete and have testing throughly. some of the issue which I am seeing and analyzing on this approach is that
- clock disable can be called from isr context or not?
- how much complexity will be added in dma driver to implement this?
- What power benefit we will get on this.
- Is there any user which generally use dma and always keep dma on requested state like UART RX always ready etc.

So keeping that in mind, it will take some time to complete this and meanwhile, I want to make it work for Tegra20 based system which is not working on current driver.
and hence this is the change.


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