[PATCH] dmaengine: at_xdmac: use module_platform_driver

[PATCH] dmaengine: at_xdmac: use module_platform_driver

[Clément Léger]

The driver was previously probed with platform_driver_probe. This does
not allow the driver to be probed again later if probe function
returns -EPROBE_DEFER. This patch replace the use of
platform_driver_probe with module_platform_driver which allows that.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
---
 drivers/dma/at_xdmac.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
index 64a52bf4d737..109a4c0895f4 100644
--- a/drivers/dma/at_xdmac.c
+++ b/drivers/dma/at_xdmac.c
@@ -2238,11 +2238,7 @@ static struct platform_driver at_xdmac_driver = {
 	}
 };
 
-static int __init at_xdmac_init(void)
-{
-	return platform_driver_probe(&at_xdmac_driver, at_xdmac_probe);
-}
-subsys_initcall(at_xdmac_init);
+module_platform_driver(at_xdmac_driver);
 
 MODULE_DESCRIPTION("Atmel Extended DMA Controller driver");
 MODULE_AUTHOR("Ludovic Desroches <ludovic.desroches@atmel.com>");
-- 
2.32.0

Re: [PATCH] dmaengine: at_xdmac: use module_platform_driver

[Vinod Koul]

On 25-06-21, 11:00, Clément Léger wrote:
> The driver was previously probed with platform_driver_probe. This does
> not allow the driver to be probed again later if probe function
> returns -EPROBE_DEFER. This patch replace the use of
> platform_driver_probe with module_platform_driver which allows that.
> 
> Signed-off-by: Clément Léger <clement.leger@bootlin.com>
> ---
>  drivers/dma/at_xdmac.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> index 64a52bf4d737..109a4c0895f4 100644
> --- a/drivers/dma/at_xdmac.c
> +++ b/drivers/dma/at_xdmac.c
> @@ -2238,11 +2238,7 @@ static struct platform_driver at_xdmac_driver = {
>  	}
>  };
>  
> -static int __init at_xdmac_init(void)
> -{
> -	return platform_driver_probe(&at_xdmac_driver, at_xdmac_probe);
> -}
> -subsys_initcall(at_xdmac_init);
> +module_platform_driver(at_xdmac_driver);

You are also changing the init call here, there is a reason why
dmaengine drivers are subsys_initcall.. have you tested this?

-- 
~Vinod

Re: [PATCH] dmaengine: at_xdmac: use module_platform_driver

[Clément Léger]

Le Wed, 28 Jul 2021 12:26:50 +0530,
Vinod Koul <vkoul@kernel.org> a écrit :

> On 25-06-21, 11:00, Clément Léger wrote:
> > The driver was previously probed with platform_driver_probe. This
> > does not allow the driver to be probed again later if probe function
> > returns -EPROBE_DEFER. This patch replace the use of
> > platform_driver_probe with module_platform_driver which allows that.
> > 
> > Signed-off-by: Clément Léger <clement.leger@bootlin.com>
> > ---
> >  drivers/dma/at_xdmac.c | 6 +-----
> >  1 file changed, 1 insertion(+), 5 deletions(-)
> > 
> > diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> > index 64a52bf4d737..109a4c0895f4 100644
> > --- a/drivers/dma/at_xdmac.c
> > +++ b/drivers/dma/at_xdmac.c
> > @@ -2238,11 +2238,7 @@ static struct platform_driver
> > at_xdmac_driver = { }
> >  };
> >  
> > -static int __init at_xdmac_init(void)
> > -{
> > -	return platform_driver_probe(&at_xdmac_driver,
> > at_xdmac_probe); -}
> > -subsys_initcall(at_xdmac_init);
> > +module_platform_driver(at_xdmac_driver);  
> 
> You are also changing the init call here, there is a reason why
> dmaengine drivers are subsys_initcall.. have you tested this?
> 

I understood that the subsys initcall was there to probe the DMA driver
earlier than other drivers (at least I guess this was the reason). I
also tested it and can confirm you this works as expected on my
platform (sama5d2_xplained and sama5d27_som1).

In my configuration, the clocks are provided using SCMI and the SCMI
driver probes them later than other drivers. 

With the current subsys_initcall, platform_driver_probe calls
__platform_driver_probe which will eventually calls platform_probe.
This one will fails because SCMI clocks are not available at this time.
And as said in the kernel doc, __platform_driver_probe is incompatible
with deferred probing. This leads to failure of all drivers that needs
DMA channels provbided by at_xdmac.

With module_platform_driver, the at_xdmac driver is correctly probed
again later and all drivers that depends on DMA channels provided by
this one are also correctly probed. The deferred probing mechanism seems
to do its job correctly (at least in my case).

Re: [PATCH] dmaengine: at_xdmac: use module_platform_driver

[Vinod Koul]

On 28-07-21, 09:38, Clément Léger wrote:
> Le Wed, 28 Jul 2021 12:26:50 +0530,
> Vinod Koul <vkoul@kernel.org> a écrit :
> 
> > On 25-06-21, 11:00, Clément Léger wrote:
> > > The driver was previously probed with platform_driver_probe. This
> > > does not allow the driver to be probed again later if probe function
> > > returns -EPROBE_DEFER. This patch replace the use of
> > > platform_driver_probe with module_platform_driver which allows that.
> > > 
> > > Signed-off-by: Clément Léger <clement.leger@bootlin.com>
> > > ---
> > >  drivers/dma/at_xdmac.c | 6 +-----
> > >  1 file changed, 1 insertion(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> > > index 64a52bf4d737..109a4c0895f4 100644
> > > --- a/drivers/dma/at_xdmac.c
> > > +++ b/drivers/dma/at_xdmac.c
> > > @@ -2238,11 +2238,7 @@ static struct platform_driver
> > > at_xdmac_driver = { }
> > >  };
> > >  
> > > -static int __init at_xdmac_init(void)
> > > -{
> > > -	return platform_driver_probe(&at_xdmac_driver,
> > > at_xdmac_probe); -}
> > > -subsys_initcall(at_xdmac_init);
> > > +module_platform_driver(at_xdmac_driver);  
> > 
> > You are also changing the init call here, there is a reason why
> > dmaengine drivers are subsys_initcall.. have you tested this?
> > 
> 
> I understood that the subsys initcall was there to probe the DMA driver
> earlier than other drivers (at least I guess this was the reason). I

That is correct

> also tested it and can confirm you this works as expected on my
> platform (sama5d2_xplained and sama5d27_som1).
> 
> In my configuration, the clocks are provided using SCMI and the SCMI
> driver probes them later than other drivers. 

Heh, clocks should get probed even earlier

> With the current subsys_initcall, platform_driver_probe calls
> __platform_driver_probe which will eventually calls platform_probe.
> This one will fails because SCMI clocks are not available at this time.
> And as said in the kernel doc, __platform_driver_probe is incompatible
> with deferred probing. This leads to failure of all drivers that needs
> DMA channels provbided by at_xdmac.
> 
> With module_platform_driver, the at_xdmac driver is correctly probed
> again later and all drivers that depends on DMA channels provided by
> this one are also correctly probed. The deferred probing mechanism seems
> to do its job correctly (at least in my case).

OK would then recommend making it like module_platform_driver ie remove
platform_driver_probe, so the defer probe would work, but keep the init
at subsys level. That should work for you while keeping this sane for
folks that dont need this

-- 
~Vinod

Re: [PATCH] dmaengine: at_xdmac: use module_platform_driver

[Clément Léger]

Le Wed, 28 Jul 2021 13:53:48 +0530,
Vinod Koul <vkoul@kernel.org> a écrit :

> On 28-07-21, 09:38, Clément Léger wrote:
> > Le Wed, 28 Jul 2021 12:26:50 +0530,
> > Vinod Koul <vkoul@kernel.org> a écrit :
> >   
> > > On 25-06-21, 11:00, Clément Léger wrote:  
> > > > The driver was previously probed with platform_driver_probe.
> > > > This does not allow the driver to be probed again later if
> > > > probe function returns -EPROBE_DEFER. This patch replace the
> > > > use of platform_driver_probe with module_platform_driver which
> > > > allows that.
> > > > 
> > > > Signed-off-by: Clément Léger <clement.leger@bootlin.com>
> > > > ---
> > > >  drivers/dma/at_xdmac.c | 6 +-----
> > > >  1 file changed, 1 insertion(+), 5 deletions(-)
> > > > 
> > > > diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> > > > index 64a52bf4d737..109a4c0895f4 100644
> > > > --- a/drivers/dma/at_xdmac.c
> > > > +++ b/drivers/dma/at_xdmac.c
> > > > @@ -2238,11 +2238,7 @@ static struct platform_driver
> > > > at_xdmac_driver = { }
> > > >  };
> > > >  
> > > > -static int __init at_xdmac_init(void)
> > > > -{
> > > > -	return platform_driver_probe(&at_xdmac_driver,
> > > > at_xdmac_probe); -}
> > > > -subsys_initcall(at_xdmac_init);
> > > > +module_platform_driver(at_xdmac_driver);    
> > > 
> > > You are also changing the init call here, there is a reason why
> > > dmaengine drivers are subsys_initcall.. have you tested this?
> > >   
> > 
> > I understood that the subsys initcall was there to probe the DMA
> > driver earlier than other drivers (at least I guess this was the
> > reason). I  
> 
> That is correct
> 
> > also tested it and can confirm you this works as expected on my
> > platform (sama5d2_xplained and sama5d27_som1).
> > 
> > In my configuration, the clocks are provided using SCMI and the SCMI
> > driver probes them later than other drivers.   
> 
> Heh, clocks should get probed even earlier

Yes, even clocksources might need them... But that's another story.

> 
> > With the current subsys_initcall, platform_driver_probe calls
> > __platform_driver_probe which will eventually calls platform_probe.
> > This one will fails because SCMI clocks are not available at this
> > time. And as said in the kernel doc, __platform_driver_probe is
> > incompatible with deferred probing. This leads to failure of all
> > drivers that needs DMA channels provbided by at_xdmac.
> > 
> > With module_platform_driver, the at_xdmac driver is correctly probed
> > again later and all drivers that depends on DMA channels provided by
> > this one are also correctly probed. The deferred probing mechanism
> > seems to do its job correctly (at least in my case).  
> 
> OK would then recommend making it like module_platform_driver ie
> remove platform_driver_probe, so the defer probe would work, but keep
> the init at subsys level. That should work for you while keeping this
> sane for folks that dont need this
> 

Ok, I'll modify it this way, thanks.



-- 
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com