linux-kernel - Re: [PATCH 2/3] drm/tegra: Deliver syncpoint base to user space

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Message-ID: <5257D1AD.9060000@nvidia.com>
Date:	Fri, 11 Oct 2013 13:23:41 +0300
From:	Arto Merilainen <amerilainen@...dia.com>
To:	Thierry Reding <thierry.reding@...il.com>
CC:	Terje Bergstrom <tbergstrom@...dia.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] drm/tegra: Deliver syncpoint base to user space

On 10/11/2013 12:43 PM, Thierry Reding wrote:
> * PGP Signed by an unknown key
>
> On Wed, Oct 09, 2013 at 02:54:09PM +0300, Arto Merilainen wrote:
>> This patch makes the necessary additions to deliver syncpoint base
>> to the user space.
>>
>> This patch splits the index field in the drm_tegra_get_syncpt structure
>> into three separate fields (index, support_base, base_id). This allows
>> to keep compatibility over kernel versions:
>> - The placing of index field stays constant and therefore the interface
>>    should stay compatible with earlier userspace versions.
>> - The old index field was input-only and it was not supposed to be read
>>    afterwards. Delivering data back in the same field should not introduce
>>    regressions to any old user space applications.
>> - Old kernels left support_base and base_id fields intact (zero) and
>>    hence the new user space applications get the correct response from
>>    the kernel (=syncpoint does not have a base).
>>
>> Signed-off-by: Arto Merilainen <amerilainen@...dia.com>
>> ---
>>   drivers/gpu/host1x/drm/drm.c | 2 ++
>>   include/uapi/drm/tegra_drm.h | 4 +++-
>>   2 files changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/host1x/drm/drm.c b/drivers/gpu/host1x/drm/drm.c
>> index 8c61cee..4251563 100644
>> --- a/drivers/gpu/host1x/drm/drm.c
>> +++ b/drivers/gpu/host1x/drm/drm.c
>> @@ -468,6 +468,8 @@ static int tegra_get_syncpt(struct drm_device *drm, void *data,
>>
>>   	syncpt = context->client->syncpts[args->index];
>>   	args->id = host1x_syncpt_id(syncpt);
>> +	args->support_base = syncpt->base ? 1 : 0;
>> +	args->base_id = syncpt->base ? syncpt->base->id : 0;
>>
>>   	return 0;
>>   }
>> diff --git a/include/uapi/drm/tegra_drm.h b/include/uapi/drm/tegra_drm.h
>> index 73bde4e..7a79ca5 100644
>> --- a/include/uapi/drm/tegra_drm.h
>> +++ b/include/uapi/drm/tegra_drm.h
>> @@ -61,7 +61,9 @@ struct drm_tegra_close_channel {
>>
>>   struct drm_tegra_get_syncpt {
>>   	__u64 context;
>> -	__u32 index;
>> +	__u16 index;
>> +	__u8 support_base;
>> +	__u8 base_id;
>>   	__u32 id;
>
> I don't like this. Can't we just add a separate IOCTL? Something like:

Sure. This felt like a good idea, but I must admit I had a bit mixed 
feelings after looking my own explanation why this would be ok...

- Arto

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