linux-kernel - Re: Re: [etnaviv-next v13 7/7] drm/etnaviv: Add support for vivante GPU cores attached via PCI(e)

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Message-ID: <jahydq72bqb27de2ijwwmdjh4ri326mxhfjn5pbvf7cqcpnauq@rw5hjdiroi5d>
Date: Thu, 8 Feb 2024 16:27:02 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Sui Jingfeng <sui.jingfeng@...ux.dev>, 
	Lucas Stach <l.stach@...gutronix.de>, Russell King <linux+etnaviv@...linux.org.uk>, 
	Christian Gmeiner <christian.gmeiner@...il.com>, David Airlie <airlied@...il.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, dri-devel@...ts.freedesktop.org, etnaviv@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org
Subject: Re: Re: [etnaviv-next v13 7/7] drm/etnaviv: Add support for vivante
 GPU cores attached via PCI(e)

On Wed, Feb 07, 2024 at 10:35:49AM +0100, Daniel Vetter wrote:
> On Wed, Feb 07, 2024 at 01:27:59AM +0800, Sui Jingfeng wrote:
> > The component helper functions are the glue, which is used to bind multiple
> > GPU cores to a virtual master platform device. Which is fine and works well
> > for the SoCs who contains multiple GPU cores.
> > 
> > The problem is that usperspace programs (such as X server and Mesa) will
> > search the PCIe device to use if it is exist. In other words, usperspace
> > programs open the PCIe device with higher priority. Creating a virtual
> > master platform device for PCI(e) GPUs is unnecessary, as the PCI device
> > has been created by the time drm/etnaviv is loaded.
> > 
> > we create virtual platform devices as a representation for the vivante GPU
> > ip core. As all of subcomponent are attached via the PCIe master device,
> > we reflect this hardware layout by binding all of the virtual child to the
> > the real master.
> > 
> > Signed-off-by: Sui Jingfeng <sui.jingfeng@...ux.dev>
> 
> Uh so my understanding is that drivers really shouldn't create platform
> devices of their own. For this case here I think the aux-bus framework is
> the right thing to use. Alternatively would be some infrastructure where
> you feed a DT tree to driver core or pci subsystem and it instantiates it
> all for you correctly, and especially with hotunplug all done right since
> this is pci now, not actually part of the soc that cannot be hotunplugged.

I don't think we need intermediate platform devices at all. We just need
to register our GPU against the PCI device and that's it. We don't need
a platform device, we don't need the component framework.

> I think I've seen some other pci devices from arm soc designs that would
> benefit from this too, so lifting this logic into a pci function would
> make sense imo.

Nouveau supports both iirc.

Maxime

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