Subject: [PATCH 3/3] ARM: imx6: Fix procedure to switch the parent of LDB_DI_CLK

From: [email-masked] (Dirk Behme)
Date: Tue, 10 Feb 2015 18:21:21 +0100

On 10.02.2015 16:31, Joshua Clayton wrote:
> On Tuesday, February 10, 2015 12:24:29 PM Dirk Behme wrote:
>> On 06.01.2015 16:47, Philipp Zabel wrote:
>>> From: Fabio Estevam <[email-masked]>
>>>
>>> Due to incorrect placement of the clock gate cell in the ldb_di[x]_clk
>>> tree, the glitchy parent mux of ldb_di[x]_clk can cause a glitch to enter
>>> the ldb_di_ipu_div divider. If the divider gets locked up, no
>>> ldb_di[x]_clk is generated, and the LVDS display will hang when the
>>> ipu_di_clk is sourced from ldb_di_clk.
>>>
>>> To fix the problem, both the new and current parent of the ldb_di_clk
>>> should be disabled before the switch. This patch ensures that correct
>>> steps are followed when ldb_di_clk parent is switched in the beginning of
>>> boot. The glitchy muxes are then registered as read-only. The clock
>>> parent can be selected using the assigned-clocks and
>>> assigned-clock-parents properties of the ccm>
>>> device tree node:
>>> 	&clks {
>>> 	
>>> 		assigned-clocks = <&clks IMX6QDL_CLK_LDB_DI0_SEL>,
>>> 		
>>> 				  <&clks IMX6QDL_CLK_LDB_DI1_SEL>;
>>> 		
>>> 		assigned-clock-parents = <&clks IMX6QDL_CLK_MMDC_CH1_AXI>,
>>> 		
>>> 					 <&clks IMX6QDL_CLK_PLL5_VIDEO_DIV>;
>>> 	
>>> 	};
>>>
>>> Signed-off-by: Ranjani Vaidyanathan <[email-masked]>
>>> Signed-off-by: Fabio Estevam <[email-masked]>
>>> Signed-off-by: Philipp Zabel <[email-masked]>
>>> ---
>>>
>>>    arch/arm/mach-imx/clk-imx6q.c | 201
>>>    ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 201
>>>    insertions(+)
>>>
>>> diff --git a/arch/arm/mach-imx/clk-imx6q.c b/arch/arm/mach-imx/clk-imx6q.c
>>> index 2e379fb..77aa7b17 100644
>>> --- a/arch/arm/mach-imx/clk-imx6q.c
>>> +++ b/arch/arm/mach-imx/clk-imx6q.c
>>
>> ...
>>
>>> +	/*
>>> +	 * The LDB_DI0/1_SEL muxes are registered read-only due to a hardware
>>> +	 * bug. Set the muxes to the requested values before registering the
>>> +	 * ldb_di_sel clocks.
>>> +	 */
>>> +	if ((imx_get_soc_revision() != IMX_CHIP_REVISION_1_0) ||
>>> +	    cpu_is_imx6dl())
>>> +		init_ldb_clks(np, base);
>>
>> I've a hopefully simple understanding question regarding this if():
>>
>> What does happen (or: has to be done) in the (non-existing) else case of
>> this if() statement?
>>
>> E.g. how to configure the clocks for the imx_get_soc_revision() ==
>> IMX_CHIP_REVISION_1_0 case?
>>
>> For the if() case, we can configure the clocks via the assigned-clocks
>> and assigned-clock-parents as described in the commit message. But how
>> to configure the clocks/muxes in the else case? To my understanding,
>> with the patch 2/3 [1] the clocks/muxes are configured to read only.
>>
>> Sorry if I missed anything ;)
>>
>> Many thanks,
>>
>> Dirk
>>
>> [1]
>> http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/313619.ht
>> ml
....
> I have at least one imx6q SoM with IMX_CHIP_REVISION_1_0, and can confirm
> that with the current mainline kernel, it gets no lvds video,

Just to avoid confusion: I don't think the patch we are talking about 
here is already in current mainline:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/log/arch/arm/mach-imx/clk-imx6q.c

I.e. the issue you describe is an other topic than the one I asked for.

Best regards

Dirk