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

[Dirk Behme]

On 10.02.2015 12:24, Dirk Behme wrote:
> On 06.01.2015 16:47, Philipp Zabel wrote:
>> From: Fabio Estevam <fabio.estevam at freescale.com>
>>
>> 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 <Ranjani.Vaidyanathan at freescale.com>
>> Signed-off-by: Fabio Estevam <fabio.estevam at freescale.com>
>> Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
>> ---
>>   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 ;)


Any ideas regarding this?

Many thanks

Dirk

> [1]
> http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/313619.html