Re: [RFC] drm: implement generic firmware eviction

From: Hans de Goede <hdegoede@redhat.com>
To: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: devicetree <devicetree@vger.kernel.org>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Rob Herring <robh+dt@kernel.org>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>
Subject: Re: [RFC] drm: implement generic firmware eviction
Date: Fri, 26 Aug 2016 14:58:51 +0200	[thread overview]
Message-ID: <ae99ee66-e3c4-8d97-0ff1-c6764e0d9d87@redhat.com> (raw)
In-Reply-To: <20160826125253.GB21452@lukather>

Hi,

On 26-08-16 14:52, Maxime Ripard wrote:
> On Fri, Aug 26, 2016 at 11:02:17AM +0200, Hans de Goede wrote:
>> Hi,
>>
>> On 26-08-16 10:58, Maxime Ripard wrote:
>>> Hi,
>>>
>>> On Fri, Aug 26, 2016 at 10:43:55AM +0200, Hans de Goede wrote:
>>>>>> I'm not sure we would want to remove the device at all, we
>>>>>> certainly should not be removing the dt_node from the devicetree
>>>>>> IMHO. Having that around to see how the bootloader set things up
>>>>>> is really useful for debugging and normally we should never modify
>>>>>> the devicetree as set up by the bootloader.
>>>>>>
>>>>>> Why not just unbind the driver from the platform device? That
>>>>>> should be enough.
>>>>>
>>>>> That will leave IORESOURCE_MEM around, causing conflicts if
>>>>> re-used/claimed by other devices/drivers. Furthermore, it is really
>>>>> fragile leaving the device around, without any control over
>>>>> possible future driver probing.
>>>>
>>>> Ah, good point. On ARM this currently typically is reserved by the bootloader
>>>> so never touched by the kernel at all, not even when the simplefb is no longer
>>>> used, actually returning this memory to the kernel after unbinding the simplefb /
>>>> destroying the simplefb platform-dev would be really good to do. We should
>>>> probably figure out how that should be done before getting rid of
>>>> remove_conflicting_framebuffers... (sorry).
>>>
>>> That would be rather easy to do. The firmware could generate a
>>> reserved-memory node instead of passing a smaller memory size to the
>>> kernel. That way, the kernel will know that it's actual ram that it
>>> can reclaim.
>>
>> So when would the kernel reclaim the RAM then?
>
> When we kickout the framebuffer driver?

Yes that is when we _want_ it to reclaim the RAM, my question was when
it will _actually_ happen ? I'm not familiar with the reserved-memory
implementation. Does your answer mean that some driver must make an
explicit call to get the memory reclaimed ?

Regards,

Hans
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