linux-kernel - Re: [PATCH] soc: imx: gpc: de-register power domains only if initialized

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Message-ID: <ca2d65f7b79df62f59942deca74e40d3@agner.ch>
Date:   Mon, 08 Jan 2018 22:17:34 +0100
From:   Stefan Agner <stefan@...er.ch>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     Dong Aisheng <dongas86@...il.com>, shawnguo@...nel.org,
        kernel@...gutronix.de, fabio.estevam@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-imx@....com
Subject: Re: [PATCH] soc: imx: gpc: de-register power domains only if
 initialized

On 2018-01-08 11:51, Lucas Stach wrote:
> Am Montag, den 08.01.2018, 18:28 +0800 schrieb Dong Aisheng:
>> On Sun, Jan 07, 2018 at 02:49:05PM +0100, Stefan Agner wrote:
>> > If power domain information are missing in the device tree, no
>> > power domains get initialized. However, imx_gpc_remove tries to
>> > remove power domains always in the old DT binding case. Only
>> > remove power domains when imx_gpc_probe initialized them in
>> > first place.
>> >
>> > Fixes: 721cabf6c660 ("soc: imx: move PGC handling to a new GPC
>> > driver")
>> > Cc: Lucas Stach <l.stach@...gutronix.de>
>> > Signed-off-by: Stefan Agner <stefan@...er.ch>
>> > ---
>> >  drivers/soc/imx/gpc.c | 10 +++++++++-
>> >  1 file changed, 9 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/soc/imx/gpc.c b/drivers/soc/imx/gpc.c
>> > index 53f7275d6cbd..62bb724726d9 100644
>> > --- a/drivers/soc/imx/gpc.c
>> > +++ b/drivers/soc/imx/gpc.c
>> > @@ -470,13 +470,21 @@ static int imx_gpc_probe(struct
>> > platform_device *pdev)
>> >  
>> >  static int imx_gpc_remove(struct platform_device *pdev)
>> >  {
>>
>> What's the original purpose of imx_gpc_remove?
>> ARM power domain can't be removed.
> 
> Why? As long as it stays powered on there is not reason why we wouldn't
> be able to remove the driver.
> 

Is it really safe to make assumptions of the hardware state when drivers
get removed? At least some drivers disable the hardware on remove (e.g.
i.MX SPI driver).

>> And why current imx_gpc_remove only remove domains for old DT but not
>> for new ones?
> 
> With the new binding the power domains will be removed by the sub-
> drivers for the domains.
> 
>> How about make it un-removable?
>> e.g.
> 
> I don't see why this would be a good idea. Once more device-dependency
> handling is in place we might need to unbind the power domains when the
> regulator driver for the domain is unbound. Do you intend to make them
> non-removable, too?

I think it would be preferable to keep the ability to remote the driver.

However, I noticed that even with this fix, with device trees which do
use the power domains capabilities (e.g. i.MX6DL) it leads to a stack
trace when using DEBUG_TEST_DRIVER_REMOVE=y, see:
https://marc.info/?l=linux-arm-kernel&m=151544599904423&w=4

--
Stefan

> 
> Regards,
> Lucas
> 
>> diff --git a/drivers/soc/imx/gpc.c b/drivers/soc/imx/gpc.c
>> index 47e7aa9..7fc6737 100644
>> --- a/drivers/soc/imx/gpc.c
>> +++ b/drivers/soc/imx/gpc.c
>> @@ -454,36 +454,17 @@ static int imx_gpc_probe(struct platform_device
>> *pdev)
>>         return 0;
>>  }
>>  
>> -static int imx_gpc_remove(struct platform_device *pdev)
>> -{
>> -       int ret;
>> -
>> -       /*
>> -        * If the old DT binding is used the toplevel driver needs to
>> -        * de-register the power domains
>> -        */
>> -       if (!of_get_child_by_name(pdev->dev.of_node, "pgc")) {
>> -               of_genpd_del_provider(pdev->dev.of_node);
>> -
>> -               ret =
>> pm_genpd_remove(&imx_gpc_domains[GPC_PGC_DOMAIN_PU].base);
>> -               if (ret)
>> -                       return ret;
>> -               imx_pgc_put_clocks(&imx_gpc_domains[GPC_PGC_DOMAIN_PU
>> ]);
>> -
>> -               ret =
>> pm_genpd_remove(&imx_gpc_domains[GPC_PGC_DOMAIN_ARM].base);
>> -               if (ret)
>> -                       return ret;
>> -       }
>> -
>> -       return 0;
>> -}
>> -
>>  static struct platform_driver imx_gpc_driver = {
>>         .driver = {
>>                 .name = "imx-gpc",
>>                 .of_match_table = imx_gpc_dt_ids,
>> +                /*
>> +                 * We can't forcibly eject devices form power
>> domain,
>> +                 * so we can't really remove power domains once they
>> +                 * were added.
>> +                 */
>> +                .suppress_bind_attrs = true,
>>         },
>>         .probe = imx_gpc_probe,
>> -       .remove = imx_gpc_remove,
>>  };
>>  builtin_platform_driver(imx_gpc_driver)
>>
>> Regards
>> Dong Aisheng
>>
>> > +	struct device_node *pgc_node;
>> >  	int ret;
>> >  
>> > +	pgc_node = of_get_child_by_name(pdev->dev.of_node, "pgc");
>> > +
>> > +	/* bail out if DT too old and doesn't provide the
>> > necessary info */
>> > +	if (!of_property_read_bool(pdev->dev.of_node, "#power-
>> > domain-cells") &&
>> > +	    !pgc_node)
>> > +		return 0;
>> > +
>> >  	/*
>> >  	 * If the old DT binding is used the toplevel driver needs
>> > to
>> >  	 * de-register the power domains
>> >  	 */
>> > -	if (!of_get_child_by_name(pdev->dev.of_node, "pgc")) {
>> > +	if (!pgc_node) {
>> >  		of_genpd_del_provider(pdev->dev.of_node);
>> >  
>> >  		ret =
>> > pm_genpd_remove(&imx_gpc_domains[GPC_PGC_DOMAIN_PU].base);
>> > -- 
>> > 2.15.1
>> >