linux-kernel - Re: [RFC PATCH 06/12] staging: android: ion: Remove crufty cache support

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Message-ID: <CACvgo52Q-HvChU7_q65GFqOaVY7Z7EaDoRfELup0D_N_ge9poQ@mail.gmail.com>
Date:   Mon, 6 Mar 2017 17:00:50 +0000
From:   Emil Velikov <emil.l.velikov@...il.com>
To:     Laura Abbott <labbott@...hat.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        devel@...verdev.osuosl.org, romlem@...gle.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
        Riley Andrews <riandrews@...roid.com>,
        Mark Brown <broonie@...nel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        LAKML <linux-arm-kernel@...ts.infradead.org>,
        linux-media@...r.kernel.org
Subject: Re: [RFC PATCH 06/12] staging: android: ion: Remove crufty cache support

On 6 March 2017 at 10:29, Daniel Vetter <daniel@...ll.ch> wrote:
> On Fri, Mar 03, 2017 at 10:46:03AM -0800, Laura Abbott wrote:
>> On 03/03/2017 08:39 AM, Laurent Pinchart wrote:
>> > Hi Daniel,
>> >
>> > On Friday 03 Mar 2017 10:56:54 Daniel Vetter wrote:
>> >> On Thu, Mar 02, 2017 at 01:44:38PM -0800, Laura Abbott wrote:
>> >>> Now that we call dma_map in the dma_buf API callbacks there is no need
>> >>> to use the existing cache APIs. Remove the sync ioctl and the existing
>> >>> bad dma_sync calls. Explicit caching can be handled with the dma_buf
>> >>> sync API.
>> >>>
>> >>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>> >>> ---
>> >>>
>> >>>  drivers/staging/android/ion/ion-ioctl.c         |  5 ----
>> >>>  drivers/staging/android/ion/ion.c               | 40 --------------------
>> >>>  drivers/staging/android/ion/ion_carveout_heap.c |  6 ----
>> >>>  drivers/staging/android/ion/ion_chunk_heap.c    |  6 ----
>> >>>  drivers/staging/android/ion/ion_page_pool.c     |  3 --
>> >>>  drivers/staging/android/ion/ion_system_heap.c   |  5 ----
>> >>>  6 files changed, 65 deletions(-)
>> >>>
>> >>> diff --git a/drivers/staging/android/ion/ion-ioctl.c
>> >>> b/drivers/staging/android/ion/ion-ioctl.c index 5b2e93f..f820d77 100644
>> >>> --- a/drivers/staging/android/ion/ion-ioctl.c
>> >>> +++ b/drivers/staging/android/ion/ion-ioctl.c
>> >>> @@ -146,11 +146,6 @@ long ion_ioctl(struct file *filp, unsigned int cmd,
>> >>> unsigned long arg)>
>> >>>                   data.handle.handle = handle->id;
>> >>>
>> >>>           break;
>> >>>
>> >>>   }
>> >>>
>> >>> - case ION_IOC_SYNC:
>> >>> - {
>> >>> -         ret = ion_sync_for_device(client, data.fd.fd);
>> >>> -         break;
>> >>> - }
>> >>
>> >> You missed the case ION_IOC_SYNC: in compat_ion.c.
>> >>
>> >> While at it: Should we also remove the entire custom_ioctl infrastructure?
>> >> It's entirely unused afaict, and for a pure buffer allocator I don't see
>> >> any need to have custom ioctl.
>> >
>> > I second that, if you want to make ion a standard API, then we certainly don't
>> > want any custom ioctl.
>> >
>> >> More code to remove potentially:
>> >> - The entire compat ioctl stuff - would be an abi break, but I guess if we
>> >>   pick the 32bit abi and clean up the uapi headers we'll be mostly fine.
>> >>   would allow us to remove compat_ion.c entirely.
>> >>
>> >> - ION_IOC_IMPORT: With this ion is purely an allocator, so not sure we
>> >>   still need to be able to import anything. All the cache flushing/mapping
>> >>   is done through dma-buf ops/ioctls.
>> >>
>> >>
>>
>> Good point to all of the above. I was considering keeping the import around
>> for backwards compatibility reasons but given how much other stuff is being
>> potentially broken, everything should just get ripped out.
>
> If you're ok with breaking the world, then I strongly suggest we go
> through the uapi header and replace all types with the standard
> fixed-width ones (__s32, __s64 and __u32, __u64). Allows us to remove all
> the compat ioctl code :-)

I think the other comments from your "botching-up ioctls" [1] also apply ;-)
Namely - align structs to multiple of 64bit, add "flags" and properly
verity user input returning -EINVAL.

-Emil

[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/ioctl/botching-up-ioctls.txt