[PATCH RESEND] drm/rockchip: Unregister platform drivers in reverse order

[PATCH RESEND] drm/rockchip: Unregister platform drivers in reverse order

[Cristian Ciocaltea]

Move rockchip_drm_platform_driver unregistration after its sub-drivers,
which ensures all drivers are unregistered in the reverse order used
when they were registered.

Fixes: 8820b68bd378 ("drm/rockchip: Refactor the component match logic.")
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
---
 drivers/gpu/drm/rockchip/rockchip_drm_drv.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
index 44d769d9234d..ca7b07503fbe 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
@@ -528,10 +528,9 @@ static int __init rockchip_drm_init(void)
 
 static void __exit rockchip_drm_fini(void)
 {
-	platform_driver_unregister(&rockchip_drm_platform_driver);
-
 	platform_unregister_drivers(rockchip_sub_drivers,
 				    num_rockchip_sub_drivers);
+	platform_driver_unregister(&rockchip_drm_platform_driver);
 }
 
 module_init(rockchip_drm_init);

---
base-commit: 1eb586a9782cde8e5091b9de74603e0a8386b09e
change-id: 20240702-rk-drm-fix-unreg-9f3f29996a00
-- 
Cristian Ciocaltea <cristian.ciocaltea@collabora.com>

Re:[PATCH RESEND] drm/rockchip: Unregister platform drivers in reverse order

[Andy Yan]

Hi Cristian,

At 2024-08-08 19:58:02, "Cristian Ciocaltea" <cristian.ciocaltea@collabora.com> wrote:
>Move rockchip_drm_platform_driver unregistration after its sub-drivers,
>which ensures all drivers are unregistered in the reverse order used
>when they were registered.

Would you please provied some detail information about how to reproduce this
issue this patch try to fix？Or some kernel log when this issue   triggered。
>
>Fixes: 8820b68bd378 ("drm/rockchip: Refactor the component match logic.")
>Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
>---
> drivers/gpu/drm/rockchip/rockchip_drm_drv.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
>diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
>index 44d769d9234d..ca7b07503fbe 100644
>--- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
>+++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
>@@ -528,10 +528,9 @@ static int __init rockchip_drm_init(void)
> 
> static void __exit rockchip_drm_fini(void)
> {
>-	platform_driver_unregister(&rockchip_drm_platform_driver);
>-
> 	platform_unregister_drivers(rockchip_sub_drivers,
> 				    num_rockchip_sub_drivers);
>+	platform_driver_unregister(&rockchip_drm_platform_driver);
> }
> 
> module_init(rockchip_drm_init);
>
>---
>base-commit: 1eb586a9782cde8e5091b9de74603e0a8386b09e
>change-id: 20240702-rk-drm-fix-unreg-9f3f29996a00
>-- 
>Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
>
>
>_______________________________________________
>Linux-rockchip mailing list
>Linux-rockchip@lists.infradead.org
>http://lists.infradead.org/mailman/listinfo/linux-rockchip

Re: [PATCH RESEND] drm/rockchip: Unregister platform drivers in reverse order

[Cristian Ciocaltea]

Hi Andy,

On 8/12/24 5:14 AM, Andy Yan wrote:
> 
> Hi Cristian,
> 
> At 2024-08-08 19:58:02, "Cristian Ciocaltea" <cristian.ciocaltea@collabora.com> wrote:
>> Move rockchip_drm_platform_driver unregistration after its sub-drivers,
>> which ensures all drivers are unregistered in the reverse order used
>> when they were registered.
> 
> Would you please provied some detail information about how to reproduce this
> issue this patch try to fix？Or some kernel log when this issue   triggered。

I submitted this patch while investigating a couple of issues
encountered when tried to reload the rockchipdrm module. 

One was a system freeze, which eventually proved to have a different
root cause and got fixed via [1].  The other one was a lockdep splat
which seems to be caused by the switch to maple tree register cache in
vop2 - I have a regmap workaround, not yet sure that's a proper fix.

As of v6.11-rc1, reloading the module works fine, w/ or w/o this patch
applied (ignoring the above mentioned splat).  But I could only verify
on Rock 3A, hence unregistering the drivers in the correct order should,
at least, eliminate a potential source of unexpected behavior on the
other boards.

Regards,
Cristian

[1]: 9d42c3ee3ce3 ("arm64: dts: rockchip: Add missing power-domains for rk356x vop_mmu")

>> Fixes: 8820b68bd378 ("drm/rockchip: Refactor the component match logic.")
>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
>> ---
>> drivers/gpu/drm/rockchip/rockchip_drm_drv.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
>> index 44d769d9234d..ca7b07503fbe 100644
>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
>> @@ -528,10 +528,9 @@ static int __init rockchip_drm_init(void)
>>
>> static void __exit rockchip_drm_fini(void)
>> {
>> -	platform_driver_unregister(&rockchip_drm_platform_driver);
>> -
>> 	platform_unregister_drivers(rockchip_sub_drivers,
>> 				    num_rockchip_sub_drivers);
>> +	platform_driver_unregister(&rockchip_drm_platform_driver);
>> }
>>
>> module_init(rockchip_drm_init);
>>
>> ---
>> base-commit: 1eb586a9782cde8e5091b9de74603e0a8386b09e
>> change-id: 20240702-rk-drm-fix-unreg-9f3f29996a00
>> -- 
>> Cristian Ciocaltea <cristian.ciocaltea@collabora.com>

Re: [PATCH RESEND] drm/rockchip: Unregister platform drivers in reverse order

[Heiko Stübner]

Am Donnerstag, 8. August 2024, 13:58:02 CEST schrieb Cristian Ciocaltea:
> Move rockchip_drm_platform_driver unregistration after its sub-drivers,
> which ensures all drivers are unregistered in the reverse order used
> when they were registered.

are you sure about that?

I.e. currently rockchip_drm_init() does 
  platform_register_drivers(rockchip_sub_drivers, ...)
to register the sub-drivers and only after that registers the main
drm-platform-driver

rockchip_drm_fini currently does the reverse of first unregistering the
main drm-platform-driver and after that unregistering the array of sub-
drivers.


So as it stands right now, rockchip_drm_fini does already do exactly the
reverse when de-registering.

> Fixes: 8820b68bd378 ("drm/rockchip: Refactor the component match logic.")
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
> ---
>  drivers/gpu/drm/rockchip/rockchip_drm_drv.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> index 44d769d9234d..ca7b07503fbe 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> @@ -528,10 +528,9 @@ static int __init rockchip_drm_init(void)
>  
>  static void __exit rockchip_drm_fini(void)
>  {
> -	platform_driver_unregister(&rockchip_drm_platform_driver);
> -
>  	platform_unregister_drivers(rockchip_sub_drivers,
>  				    num_rockchip_sub_drivers);
> +	platform_driver_unregister(&rockchip_drm_platform_driver);
>  }
>  
>  module_init(rockchip_drm_init);
> 
> ---
> base-commit: 1eb586a9782cde8e5091b9de74603e0a8386b09e
> change-id: 20240702-rk-drm-fix-unreg-9f3f29996a00
> 

Re: [PATCH RESEND] drm/rockchip: Unregister platform drivers in reverse order

[Cristian Ciocaltea]

On 8/15/24 5:21 PM, Heiko Stübner wrote:
> Am Donnerstag, 8. August 2024, 13:58:02 CEST schrieb Cristian Ciocaltea:
>> Move rockchip_drm_platform_driver unregistration after its sub-drivers,
>> which ensures all drivers are unregistered in the reverse order used
>> when they were registered.
> 
> are you sure about that?
> 
> I.e. currently rockchip_drm_init() does 
>   platform_register_drivers(rockchip_sub_drivers, ...)
> to register the sub-drivers and only after that registers the main
> drm-platform-driver
> 
> rockchip_drm_fini currently does the reverse of first unregistering the
> main drm-platform-driver and after that unregistering the array of sub-
> drivers.
> 
> 
> So as it stands right now, rockchip_drm_fini does already do exactly the
> reverse when de-registering.

Indeed, somehow I overlooked this while debugging some module unloading
issues.  I guess it just felt more naturally to have the subdrivers
unregistered first.

Out of curiosity to see if there's a common pattern for handling this, I
found that most drivers do indeed unregister the subdrivers before the main
platform one, but weirdly enough, some of them do also keep the same order
on registration, similarily to what this patch unintentionally does:

  drivers/power/supply/ab8500_charger.c
  drivers/gpu/drm/vc4/vc4_drv.c
  drivers/gpu/drm/mcde/mcde_drv.c

Not sure if those are potential mistakes, or maybe it doesn't really matter?!

Please let me know if you have a preference for it, and I'll update the
patch accordingly, otherwise let's just ignore it altogether.

Thanks,
Cristian

Re: [PATCH RESEND] drm/rockchip: Unregister platform drivers in reverse order

[Heiko Stübner]

Am Donnerstag, 15. August 2024, 19:26:54 CEST schrieb Cristian Ciocaltea:
> On 8/15/24 5:21 PM, Heiko Stübner wrote:
> > Am Donnerstag, 8. August 2024, 13:58:02 CEST schrieb Cristian Ciocaltea:
> >> Move rockchip_drm_platform_driver unregistration after its sub-drivers,
> >> which ensures all drivers are unregistered in the reverse order used
> >> when they were registered.
> > 
> > are you sure about that?
> > 
> > I.e. currently rockchip_drm_init() does 
> >   platform_register_drivers(rockchip_sub_drivers, ...)
> > to register the sub-drivers and only after that registers the main
> > drm-platform-driver
> > 
> > rockchip_drm_fini currently does the reverse of first unregistering the
> > main drm-platform-driver and after that unregistering the array of sub-
> > drivers.
> > 
> > 
> > So as it stands right now, rockchip_drm_fini does already do exactly the
> > reverse when de-registering.
> 
> Indeed, somehow I overlooked this while debugging some module unloading
> issues.  I guess it just felt more naturally to have the subdrivers
> unregistered first.
> 
> Out of curiosity to see if there's a common pattern for handling this, I
> found that most drivers do indeed unregister the subdrivers before the main
> platform one, but weirdly enough, some of them do also keep the same order
> on registration, similarily to what this patch unintentionally does:
> 
>   drivers/power/supply/ab8500_charger.c
>   drivers/gpu/drm/vc4/vc4_drv.c
>   drivers/gpu/drm/mcde/mcde_drv.c
> 
> Not sure if those are potential mistakes, or maybe it doesn't really matter?!
> 
> Please let me know if you have a preference for it, and I'll update the
> patch accordingly, otherwise let's just ignore it altogether.

in theory it shouldn't matter, simply because the component framework
will only bind when all driver are present and unbind when the first driver
vanishes.

But I really like doing the reverse order more - so as it is now.

You also wouldn't disable clocks, before trying to deactivate some device-
function.

So deactivating stuff in the reverse order of them getting activated is most
likely less error prone.