linux-kernel - Consider moving the init of pl330 to earlier?

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Date:	Thu, 9 Oct 2014 14:35:11 -0700
From:	Ray Jui <rjui@...adcom.com>
To:	Dan Williams <djbw@...com>, Vinod Koul <vinod.koul@...el.com>
CC:	Scott Branden <sbranden@...adcom.com>, Ray Jui <rjui@...adcom.com>,
	<linux-kernel@...r.kernel.org>
Subject: Consider moving the init of pl330 to earlier?

Hi,

How do you guys like the idea of moving the driver initialization of the 
pl330 DMA driver to earlier? For example, to arch_initcall_sync or 
subsys_initcall? Currently the pl330 driver is registered through 
module_amba_driver call, which translates to device_initcall in the end. 
This is a bit late considering in many systems, DMA controller is one of 
the core components that may have many slave devices depending on. Most 
slave drivers are typically done at device_initcall. When done at the 
same level, DMA may not be ready while the slave devices are being 
initialized. In addition, under the drivers/dma directory, we currently 
have various other DMA drivers also done at subsys_initcall.

One issue that I'm seeing with the Broadcom Cygnus SoC is that, when we 
try to use DMA with SPI (PL022), the request for DMA channel would fail 
because the spi-pl022 driver we use is initialized at subsys_initcall. 
At the time the PL330 driver is not yet initialized. The reason why 
spi-pl022 is done at subsys_initcall is that some regulators communicate 
through the SPI bus so people decided to move it to earlier (commit 
25c8e03b by Linus Walleij), which seems to be a valid reason to me.

Thanks,

Ray
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