linux-kernel - Re: [PATCH] spi/rockchip: Make sure spi clk is on in rockchip_spi_set

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Date:	Fri, 26 Feb 2016 10:31:50 +0800
From:	"Huang, Tao" <huangtao@...k-chips.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	Huibin Hong <huibin.hong@...k-chips.com>,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	"shawn.lin" <shawn.lin@...nel-upstream.org>,
	linux-rockchip@...ts.infradead.org,
	Addy Ke <addy.ke@...k-chips.com>
Subject: Re: [PATCH] spi/rockchip: Make sure spi clk is on in
 rockchip_spi_set_cs

On 2016年02月26日 09:58, Mark Brown wrote:
> 
>> Another way to solve this bug is add runtime PM support while spi setup.
>> Some other chips may have some problem, for example mt65xx and orion,
>> which access hardware register too.
> 
> No, this is telling you you're doing something wrong - setup() might be
> called while another transfer is in progress so you shouldn't be
> changing the hardware setup (see Documentation/spi/spi-summary).  This
> means that you normally shouldn't be writing to registers there.  Moving
> this to prepare_message() instead is probably what you want.
> 
You misunderstand me. I talk about spi_setup, as
Documentation/spi/spi-summary, which would normally be called from
probe() before the first I/O is done to the device.
spi_setup will call spi_set_cs(spi, false), which introduced with commit
1a7b7ee72c21 ("spi: Ensure that CS line is in non-active state after
spi_setup()"). And spi_set_cs will call spi->master->set_cs, and set_cs
callback will access register. Without clk enable, I believe some
drivers will failed to run.

Best Regards,

Huang, Tao