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

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Date:   Mon, 6 Mar 2017 11:29:59 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        dri-devel@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>,
        devel@...verdev.osuosl.org, romlem@...gle.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        arve@...roid.com, 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>,
        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 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 :-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch