[EXTERNAL] Re: [PATCH v3 03/14] drm/panthor: Add the device logical block

[Donald Robson]

Thanks for the bug report!
Donald

On Thu, 2023-12-07 at 10:23 +0000, Steven Price wrote:
> *** CAUTION: This email originates from a source not known to Imagination Technologies. Think before you click a link or open an attachment ***
> 
> On 07/12/2023 08:56, Boris Brezillon wrote:
> > On Thu, 7 Dec 2023 09:12:43 +0100
> > Boris Brezillon <boris.brezillon at collabora.com> wrote:
> > 
> > > On Wed, 6 Dec 2023 16:55:42 +0000
> > > Steven Price <steven.price at arm.com> wrote:
> > > 
> > > > On 04/12/2023 17:32, Boris Brezillon wrote:  
> > > > > The panthor driver is designed in a modular way, where each logical
> > > > > block is dealing with a specific HW-block or software feature. In order
> > > > > for those blocks to communicate with each other, we need a central
> > > > > panthor_device collecting all the blocks, and exposing some common
> > > > > features, like interrupt handling, power management, reset, ...
> > > > > 
> > > > > This what this panthor_device logical block is about.
> > > > > 
> > > > > v3:
> > > > > - Add acks for the MIT+GPL2 relicensing
> > > > > - Fix 32-bit support
> > > > > - Shorten the sections protected by panthor_device::pm::mmio_lock to fix
> > > > >   lock ordering issues.
> > > > > - Rename panthor_device::pm::lock into panthor_device::pm::mmio_lock to
> > > > >   better reflect what this lock is protecting
> > > > > - Use dev_err_probe()
> > > > > - Make sure we call drm_dev_exit() when something fails half-way in
> > > > >   panthor_device_reset_work()
> > > > > - Replace CSF_GPU_LATEST_FLUSH_ID_DEFAULT with a constant '1' and a
> > > > >   comment to explain. Also remove setting the dummy flush ID on suspend.
> > > > > - Remove drm_WARN_ON() in panthor_exception_name()
> > > > > - Check pirq->suspended in panthor_xxx_irq_raw_handler()
> > > > > 
> > > > > Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
> > > > > Signed-off-by: Steven Price <steven.price at arm.com>
> > > > > Acked-by: Steven Price <steven.price at arm.com> # MIT+GPL2 relicensing,Arm
> > > > > Acked-by: Grant Likely <grant.likely at linaro.org> # MIT+GPL2 relicensing,Linaro
> > > > > Acked-by: Boris Brezillon <boris.brezillon at collabora.com> # MIT+GPL2 relicensing,Collabora    
> > > > 
> > > > We still have the "FIXME: this is racy"  
> > > 
> > > Yeah, I still didn't find a proper solution for that.
> > 
> > This [1] should fix the race condition in the unplug path.
> > 
> > [1]https://urldefense.com/v3/__https://gitlab.freedesktop.org/panfrost/linux/-/commit/b79b28069e524ae7fea22a9a158b870eab2d5f9a__;!!KCwjcDI!1x9mqPx9K2SprWdgzBBRExLDu8uVajVeJcmlMkMufmIqJi5TYLqiDhhBr1hlnBQQUVgHnJKnWInjn7rWq0H_iLg$ 
> 
> Looks like it should do the job. I'm surprised that we're the only ones
> to face this though.
> 
> Looking at the new imagination driver it appears there's a similar problem:
> 
> pvr_device_lost() uses a boolean 'lost' to track multiple calls but that
> boolean isn't protected by any specific lock (AFAICT). Indeed
> pvr_device_lost() calls drm_dev_unplug() while in a drm_dev_enter()
> critical section (see pvr_mmu_flush_exec()). If I'm not mistaken that's
> the same problem we discussed and isn't allowed? drm_dev_unplug() will
> synchronise on the SRCU that drm_dev_enter() is holding.
> 
> +CC: Frank, Donald, Matt from Imagination.
> 
> Steve
>