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

[Fabio Estevam]

Hi Stephen,

On Fri, Sep 16, 2016 at 11:36 AM, Fabio Estevam <fabio.estevam at nxp.com> wrote:
> 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>;
>         };
>
> The issue is explained in detail in EB821 ("LDB Clock Switch Procedure &
> i.MX6 Asynchronous Clock Switching Guidelines") [1].
>
> [1] http://www.nxp.com/files/32bit/doc/eng_bulletin/EB821.pdf
>
> Signed-off-by: Ranjani Vaidyanathan <Ranjani.Vaidyanathan at nxp.com>
> Signed-off-by: Fabio Estevam <fabio.estevam at nxp.com>
> Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
> Reviewed-by: Akshay Bhat <akshay.bhat at timesys.com>
> Tested-by Joshua Clayton <stillcompiling at gmail.com>
> Tested-by: Charles Kang <Charles.Kang at advantech.com.tw>
> Acked-by: Shawn Guo <shawnguo at kernel.org>

Do you think this one could be applied to clk-next? It fixes an
important LVDS bug.

Thanks