Re: [PATCH 1/2] power-domain: Add support for refcounting (again)

[Neha Malcom Francis <n-francis@ti.com>]

Hi Miquel

On 25/04/25 12:19, Miquel Raynal wrote:
> It is very surprising that such an uclass, specifically designed to
> handle resources that may be shared by different devices, is not keeping
> the count of the number of times a power domain has been
> enabled/disabled to avoid shutting it down unexpectedly or disabling it
> several times.
> 
> Doing this causes troubles on eg. i.MX8MP because disabling power
> domains can be done in recursive loops were the same power domain
> disabled up to 4 times in a row. PGCs seem to have tight FSM internal
> timings to respect and it is easy to produce a race condition that puts
> the power domains in an unstable state, leading to ADB400 errors and
> later crashes in Linux.
> 
> Some drivers implement their own mechanism for that, but it is probably
> best to add this feature in the uclass and share the common code across
> drivers. In order to avoid breaking existing drivers, refcounting is
> only enabled if the number of subdomains a device node supports is
> explicitly set in the probe function. ->xlate() callbacks will return
> the power domain ID which is then being used as the array index to reach
> the correct refcounter.
> 
> As we do not want to break existing users while stile getting
> interesting error codes, the implementation is split between:
> - a low-level helper reporting error codes if the requested transition
>   could not be operated,
> - a higher-level helper ignoring the "non error" codes, like EALREADY and
>   EBUSY.
> 
> CI tests using power domains are slightly updated to make sure the count
> of on/off calls is even and the results match what we *now* expect. They
> are also extended to test the low-level functions.
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> ---
>  arch/sandbox/include/asm/power-domain.h          |  2 +
>  drivers/firmware/scmi/sandbox-scmi_devices.c     |  1 +
>  drivers/power/domain/power-domain-uclass.c       | 90 ++++++++++++++++++++++--
>  drivers/power/domain/sandbox-power-domain-test.c | 15 ++++
>  drivers/power/domain/sandbox-power-domain.c      |  4 ++
>  include/power-domain.h                           | 69 +++++++++++++++---
>  test/dm/power-domain.c                           | 11 ++-
>  7 files changed, 177 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/sandbox/include/asm/power-domain.h b/arch/sandbox/include/asm/power-domain.h
> index 4d5e861dbce2b6434ac9bcffe5fc8f704d32e62d..3b0717f8fa06f1c0493fe6ee758e2e72ff77141e 100644
> --- a/arch/sandbox/include/asm/power-domain.h
> +++ b/arch/sandbox/include/asm/power-domain.h
> @@ -13,6 +13,8 @@ int sandbox_power_domain_query(struct udevice *dev, unsigned long id);
>  int sandbox_power_domain_test_get(struct udevice *dev);
>  int sandbox_power_domain_test_on(struct udevice *dev);
>  int sandbox_power_domain_test_off(struct udevice *dev);
> +int sandbox_power_domain_test_on_ll(struct udevice *dev);
> +int sandbox_power_domain_test_off_ll(struct udevice *dev);
>  int sandbox_power_domain_test_free(struct udevice *dev);
>  
>  #endif
> diff --git a/drivers/firmware/scmi/sandbox-scmi_devices.c b/drivers/firmware/scmi/sandbox-scmi_devices.c
> index 96c2922b067e2886b3fa963bcd7e396f4569a569..9f253b0fd40f703a5ec11d34c197423d27ad8b01 100644
> --- a/drivers/firmware/scmi/sandbox-scmi_devices.c
> +++ b/drivers/firmware/scmi/sandbox-scmi_devices.c
> @@ -163,4 +163,5 @@ U_BOOT_DRIVER(sandbox_scmi_devices) = {
>  	.priv_auto = sizeof(struct sandbox_scmi_device_priv),
>  	.remove = sandbox_scmi_devices_remove,
>  	.probe = sandbox_scmi_devices_probe,
> +	.flags = DM_FLAG_DEFAULT_PD_CTRL_OFF,
>  };
[...]

Thanks for working on this quickly, I've booted it on j784s4-evm and
works fine! And I am good with this approach using subdomains.

Tested-by: Neha Malcom Francis <n-francis@ti.com>
(on j784s4-evm)

-- 
Thanking You
Neha Malcom Francis