linux-kernel - Re: [PATCH] dmaengine: pl300: enable the clock to PL330 dma

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Date:	Mon, 4 May 2015 08:28:51 -0500
From:	Dinh Nguyen <dinguyen@...nsource.altera.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
CC:	<dan.j.williams@...el.com>, <dinh.linux@...il.com>,
	<vinod.koul@...el.com>, <dmaengine@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dmaengine: pl300: enable the clock to PL330 dma

Hi Krzystof,

On 5/4/15 12:30 AM, Krzysztof Kozlowski wrote:
> 2015-05-04 13:28 GMT+09:00  <dinguyen@...nsource.altera.com>:
>> From: Dinh Nguyen <dinguyen@...nsource.altera.com>
>>
>> Turn on the clock to the PL330 DMA if there is a clock node provided.
> 
> Why? There is no explanation in the patch for this important question - why?
> 
> Amba bus already does this and provide a wrapper function.
> Additionally that would mess up with runtime PM and clock
> enable/disable.

I don't see the clock for the DMA getting turned on at all, which is why
after the kernel has booted, the filesystem tries to open up a serial
port using DMA and the system hangs. The failure is seen here:

http://arm-soc.lixom.net/bootlogs/next/next-20150504/socfpga-arm-multi_v7_defconfig.html

This only happens with the multi_v7_defconfig, because the PL330 DMA is
getting built into the kernel, while the socfpga_defconfig does not
enable the PL330.

The DTS for the socfpga platform looks like this:

pdma: pdma@...01000 {
	compatible = "arm,pl330", "arm,primecell";
	reg = <0xffe01000 0x1000>;
	interrupts = <0 104 4>,
		    <0 105 4>,
		...
		#dma-cells = <1>;
		#dma-channels = <8>;
		#dma-requests = <32>;
		clocks = <&l4_main_clk>;
		clock-names = "apb_pclk";
};

Perhaps I have the wrong designation for clock-names and the amba bus is
not able to pick up the correct clock?

Dinh

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