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Message-ID: <6d287bbb1733814009dfeb7d48f08cb6f44dc56c.camel@pengutronix.de>
Subject: Re: [PATCH v10 03/11] drm/etnaviv: Add dedicated functions to
 create and destroy platform device
From:   Lucas Stach <l.stach@pengutronix.de>
To:     Sui Jingfeng <suijingfeng@loongson.cn>,
        Sui Jingfeng <18949883232@163.com>,
        Russell King <linux+etnaviv@armlinux.org.uk>,
        Christian Gmeiner <christian.gmeiner@gmail.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>
Cc:     Bjorn Helgaas <bhelgaas@google.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        etnaviv@lists.freedesktop.org
Date:   Wed, 21 Jun 2023 12:23:35 +0200
In-Reply-To: <1c7596fd-7e63-6719-2574-7d7820687832@loongson.cn>
References: <20230620094716.2231414-1-18949883232@163.com>
         <20230620094716.2231414-4-18949883232@163.com>
         <0daa7182d6600a24988d1c81cf8fe3c0c9487f52.camel@pengutronix.de>
         <1c7596fd-7e63-6719-2574-7d7820687832@loongson.cn>
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Am Mittwoch, dem 21.06.2023 um 17:49 +0800 schrieb Sui Jingfeng:
> Hi
> 
> On 2023/6/21 17:15, Lucas Stach wrote:
> > Am Dienstag, dem 20.06.2023 um 17:47 +0800 schrieb Sui Jingfeng:
> > > From: Sui Jingfeng <suijingfeng@loongson.cn>
> > > 
> > > Also rename the virtual master platform device as etnaviv_platform_device,
> > > for better reflection that it is a platform device, not a DRM device.
> > > 
> > > Another benefit is that we no longer need to call of_node_put() for three
> > > different cases, Instead, we only need to call it once.
> > > 
> > > Cc: Lucas Stach <l.stach@pengutronix.de>
> > > Cc: Christian Gmeiner <christian.gmeiner@gmail.com>
> > > Cc: Philipp Zabel <p.zabel@pengutronix.de>
> > > Cc: Bjorn Helgaas <bhelgaas@google.com>
> > > Cc: Daniel Vetter <daniel@ffwll.ch>
> > > Signed-off-by: Sui Jingfeng <suijingfeng@loongson.cn>
> > > ---
> > >   drivers/gpu/drm/etnaviv/etnaviv_drv.c | 56 +++++++++++++++++++--------
> > >   1 file changed, 39 insertions(+), 17 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_drv.c b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
> > > index 31a7f59ccb49..cec005035d0e 100644
> > > --- a/drivers/gpu/drm/etnaviv/etnaviv_drv.c
> > > +++ b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
> > > @@ -656,12 +656,44 @@ static struct platform_driver etnaviv_platform_driver = {
> > >   	},
> > >   };
> > >   
> > > -static struct platform_device *etnaviv_drm;
> > > +static struct platform_device *etnaviv_platform_device;
> > >   
> > > -static int __init etnaviv_init(void)
> > > +static int etnaviv_create_platform_device(const char *name,
> > > +					  struct platform_device **ppdev)
> > As the platform device is a global static variable, there is no need to
> > push it through the parameters of this function. Just use the global
> > variable directly in this function.
> 
> A function reference a global static variable is *NOT* a *pure* fucntion,
> 
That's right, but all you do with those indirections through the
parameter list is move which of the functions is non-pure, in your case
it's etnaviv_init/etnaviv_exit, with the indirection dropped it's
etnaviv_create_platform_device/etnaviv_destroy_platform_device.

> it degenerate as a procedure,
> 
> 
> The function is perfect in the sense that it does not reference any 
> global variable.
> 
> 
> etnaviv_create_platform_device() is NOT intended to used by one function,
> 
> a specific purpose only, but when create this function, I want to create other
> 
> platform device with this function.
> 
> Say, You want to create a dummy platform device, targeting to bind to the real master
> 
> (the single GPU core) . To verify the idea that we choose the first 3D gpu core as master,
> 
> other 2D or VG gpu core is not as important as the 3D one.
> 
> The should bind to the 3D GPU core (master).
> 
Sorry, I'm not following what you are trying to tell me here. Could you
please rephrase?

> 
> While back to the question you ask, I want etnaviv_create_platform_device() to be generic,
> 
> can be used by multiple place for multiple purpose.
> 
> I have successfully copy this to a another drm driver by simply renaming.
> 
> The body of the function itself does not need to change.

But it isn't shared, in this compilation unit this function is specific
to the etnaviv driver and I don't see why we shouldn't have etnaviv
specifics in there if it makes the code of this driver easier to
follow.

Regards,
Lucas

> 
> > >   {
> > >   	struct platform_device *pdev;
> > >   	int ret;
> > > +
> > > +	pdev = platform_device_alloc(name, PLATFORM_DEVID_NONE);
> > > +	if (!pdev)
> > > +		return -ENOMEM;
> > > +
> > > +	ret = platform_device_add(pdev);
> > > +	if (ret) {
> > > +		platform_device_put(pdev);
> > > +		return ret;
> > > +	}
> > > +
> > > +	*ppdev = pdev;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static void etnaviv_destroy_platform_device(struct platform_device **ppdev)
> > > +{
> > > +	struct platform_device *pdev = *ppdev;
> > Same here, just use the global variable directly.
> > 
> > Regards,
> > Lucas
> > 
> > > +
> > > +	if (!pdev)
> > > +		return;
> > > +
> > > +	platform_device_unregister(pdev);
> > > +
> > > +	*ppdev = NULL;
> > > +}
> > > +
> > > +static int __init etnaviv_init(void)
> > > +{
> > > +	int ret;
> > >   	struct device_node *np;
> > >   
> > >   	etnaviv_validate_init();
> > > @@ -681,23 +713,13 @@ static int __init etnaviv_init(void)
> > >   	for_each_compatible_node(np, NULL, "vivante,gc") {
> > >   		if (!of_device_is_available(np))
> > >   			continue;
> > > +		of_node_put(np);
> > >   
> > > -		pdev = platform_device_alloc("etnaviv", PLATFORM_DEVID_NONE);
> > > -		if (!pdev) {
> > > -			ret = -ENOMEM;
> > > -			of_node_put(np);
> > > -			goto unregister_platform_driver;
> > > -		}
> > > -
> > > -		ret = platform_device_add(pdev);
> > > -		if (ret) {
> > > -			platform_device_put(pdev);
> > > -			of_node_put(np);
> > > +		ret = etnaviv_create_platform_device("etnaviv",
> > > +						     &etnaviv_platform_device);
> > > +		if (ret)
> > >   			goto unregister_platform_driver;
> > > -		}
> > >   
> > > -		etnaviv_drm = pdev;
> > > -		of_node_put(np);
> > >   		break;
> > >   	}
> > >   
> > > @@ -713,7 +735,7 @@ module_init(etnaviv_init);
> > >   
> > >   static void __exit etnaviv_exit(void)
> > >   {
> > > -	platform_device_unregister(etnaviv_drm);
> > > +	etnaviv_destroy_platform_device(&etnaviv_platform_device);
> > >   	platform_driver_unregister(&etnaviv_platform_driver);
> > >   	platform_driver_unregister(&etnaviv_gpu_driver);
> > >   }
>