linux-kernel - Re: [Linaro-mm-sig] Re: [PATCH v2 4/4] drm/nvdla/uapi: Add UAPI of NVDLA driver

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Date:   Tue, 26 Apr 2022 20:24:04 +0800
From:   Cai Huoqing <cai.huoqing@...ux.dev>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Christian König <christian.koenig@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        linaro-mm-sig@...ts.linaro.org
Subject: Re: [Linaro-mm-sig] Re: [PATCH v2 4/4] drm/nvdla/uapi: Add UAPI of
 NVDLA driver

On 26 4月 22 12:50:50, Arnd Bergmann wrote:
> On Tue, Apr 26, 2022 at 8:31 AM Christian König
> <christian.koenig@....com> wrote:
> > Am 26.04.22 um 08:08 schrieb Cai Huoqing:
> > > The NVIDIA Deep Learning Accelerator (NVDLA) is an open source IP
> > > which is integrated into NVIDIA Jetson AGX Xavier,
> > > so add UAPI of this driver.
> > >
> > > Signed-off-by: Cai Huoqing <cai.huoqing@...ux.dev>
> 
> I saw the reply but no the original mail, so I'll comment here
Hi, thanks for your reply
The patches here:
https://lore.kernel.org/lkml/20220426060808.78225-3-cai.huoqing@linux.dev/
> 
> > > +
> > > +#if !defined(__KERNEL__)
> > > +#define __user
> > > +#endif
> 
> This is done in the 'make headers_install' step, no need to define it
> separately.
> 
> > > +#define NVDLA_NO_TIMEOUT    (0xffffffff)
> > > +     __u32 timeout;
> >
> > What format does that timeout value have?
> >
> > In general it is best practice to have absolute 64bit nanosecond
> > timeouts (to be used with ktime inside the kernel) so that restarting
> > interrupted IOCTLs works smooth.
> 
> When using absolute values, one also needs to decide whether this should be
> realtime, monotonic or boottime and document the decision.
> 
> 
> > > + * struct nvdla_submit_args structure for task submit
> > > + *
> > > + * @tasks            pointer to array of struct nvdla_ioctl_submit_task
> > > + * @num_tasks                number of entries in tasks
> > > + * @flags            flags for task submit, no flags defined yet
> > > + * @version          version of task structure
> > > + *
> > > + */
> > > +struct nvdla_submit_args {
> > > +     __u64 tasks;
> > > +     __u16 num_tasks;
> > > +#define NVDLA_MAX_TASKS_PER_SUBMIT   24
> > > +#define NVDLA_SUBMIT_FLAGS_ATOMIC    (1 << 0)
> >
> > Well that "no flags defined yet" from the comment above is probably
> > outdated :)
> 
> > > +     __u16 flags;
> > > +     __u32 version;
> > > +};
> 
> Versioned interfaces are usually a bad idea. If you introduce an ioctl command,
> it should generally keep working. If you ever need to change the interface, just
> use a new command number for the new version.
> 
> > > +/**
> > > + * struct nvdla_gem_create_args for allocating DMA buffer through GEM
> > > + *
> > > + * @handle           handle updated by kernel after allocation
> > > + * @flags            implementation specific flags
> > > + * @size             size of buffer to allocate
> > > + */
> > > +struct nvdla_gem_create_args {
> > > +     __u32 handle;
> > > +     __u32 flags;
> > > +     __u64 size;
> > > +};
> > > +
> > > +/**
> > > + * struct nvdla_gem_map_offset_args for mapping DMA buffer
> > > + *
> > > + * @handle           handle of the buffer
> > > + * @reserved         reserved for padding
> > > + * @offset           offset updated by kernel after mapping
> > > + */
> > > +struct nvdla_gem_map_offset_args {
> > > +     __u32 handle;
> > > +     __u32 reserved;
> > > +     __u64 offset;
> > > +};
> > > +
> > > +#define DRM_NVDLA_SUBMIT             0x00
> > > +#define DRM_NVDLA_GEM_CREATE 0x01
> > > +#define DRM_NVDLA_GEM_MMAP           0x02
> 
> Is this an actual mmap() call, or something that needs to be done before the
> mmap()? Is the 'handle' a file descriptor or some internal number?
It's an gem object mmap which calls drm_gem_dumb_map_offset() inside and
the handle is gem object handle.

Thanks,
Cai
> 
>       Arnd