[PATCH master 2/2] pwm: imx: enable clocks during PWM register accesses

[Marco Felsch]

On 23-09-04, Ahmad Fatoum wrote:
> This is a port of Linux commit 9f4c8f9607c3147d291b70c13dd01c738ed41faf:
> 
> | Author:     Anson Huang <anson.huang at nxp.com>
> | AuthorDate: Wed Dec 19 05:24:58 2018 +0000
> | Commit:     Thierry Reding <thierry.reding at gmail.com>
> | CommitDate: Mon Dec 24 12:06:56 2018 +0100
> |
> |     pwm: imx: Add ipg clock operation
> |
> |     i.MX PWM module's ipg_clk_s is for PWM register access, on most of i.MX
> |     SoCs, this ipg_clk_s is from system ipg clock or perclk which is always
> |     enabled, but on i.MX7D, the ipg_clk_s is from PWM1_CLK_ROOT which is
> |     controlled by CCGR132, that means the CCGR132 MUST be enabled first
> |     before accessing PWM registers on i.MX7D. This patch adds ipg clock
> |     operation to make sure register access successfully on i.MX7D and it
> |     fixes Linux kernel boot up hang during PWM driver probe.
> |
> |     Fixes: 4a23e6ee9f69 ("ARM: dts: imx7d-sdb: Restore pwm backlight support")
> |     Signed-off-by: Anson Huang <Anson.Huang at nxp.com>
> |     Signed-off-by: Thierry Reding <thierry.reding at gmail.com>
> 
> Unlike the Linux version, we make clk_ipg optional to reduce changes for
> older SoCs.
> 
> This fixes system hang during PWM access on i.MX8M and presumably i.MX7.
> 
> Reported-by: Bastian Krause <bst at pengutronix.de>
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>

Reviewed-by: Marco Felsch <m.felsch at pengutronix.de>