Handle pwm with sysfs with recent kernel

[Arthur LAMBERT <lambertarthur22@gmail.com>]

I am trying to update my kernel bsp from v4.1.X to v4.19.8 but I have some regressions
when I try to use pwm through sysfs from userspace. I have three pwm declared as
follow in my device tree :

	leds {
	     compatible = "pwm-leds";
	     ledred {
		pwms = <&pwm1>;
		label = "red";
		linux,default-trigger = "none";
		default-state = "on";
	     };

	     ledblue {
	     	pwms = <&pwm5>;
		label = "blue";
		linux,default-trigger = "none";
		default-state = "on";
	     };

	     ledgreen {
	     	pwms = <&pwm6>;
		label = "green";
		linux,default-trigger = "none";
		default-state = "on";
	     };
	};

First I have an issue with duplicate name :
sysfs: cannot create duplicate filename '/class/pwm/pwm0'
CPU: 0 PID: 653 Comm: XXXX
Hardware name: Freescale i.MX6 Ultralite (Device Tree)
[<8010dda8>] (unwind_backtrace) from [<8010b468>] (show_stack+0x10/0x14)
[<8010b468>] (show_stack) from [<8025ef0c>] (sysfs_warn_dup+0x58/0x64)
[<8025ef0c>] (sysfs_warn_dup) from [<8025f200>] (sysfs_do_create_link_sd+0xd4/0xd8)
[<8025f200>] (sysfs_do_create_link_sd) from [<80458d6c>] (device_add+0x1ec/0x5d4)
[<80458d6c>] (device_add) from [<8040b5a8>] (export_store+0xfc/0x17c)
[<8040b5a8>] (export_store) from [<80456904>] (dev_attr_store+0x18/0x24)
[<80456904>] (dev_attr_store) from [<8025e604>] (sysfs_kf_write+0x44/0x48)
[<8025e604>] (sysfs_kf_write) from [<8025dcb0>] (kernfs_fop_write+0xe8/0x1d0)
[<8025dcb0>] (kernfs_fop_write) from [<801eaaf8>] (__vfs_write+0x28/0x144)
[<801eaaf8>] (__vfs_write) from [<801ead88>] (vfs_write+0xa4/0x164)
[<801ead88>] (vfs_write) from [<801eaf54>] (ksys_write+0x40/0x94)
[<801eaf54>] (ksys_write) from [<80101000>] (ret_fast_syscall+0x0

I was able to fix it by revert a patch : https://patchwork.kernel.org/patch/9971821/
It is normal that this revert patch is not currently apply on last 4.19.X tag (last one
seems to be 4.19.13)

Then I have another issue when I try to enable my pwm :

# ls /sys/class/pwm/
pwmchip0  pwmchip2  pwmchip4  pwmchip6
pwmchip1  pwmchip3  pwmchip5  pwmchip7
# echo 0 > /sys/class/pwm/pwmchip0/export
# echo 1 > /sys/class/pwm/pwmchip0/pwm0/enable
-sh: write error: Invalid argument

Is there a new way to handle pwm in recent kernel ? My old process is now deprecated or something ?

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