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Message-ID: <38382016-4769-411d-b0bf-35ce05753abd@xs4all.nl>
Date: Wed, 8 Nov 2023 11:31:22 +0100
From: Hans Verkuil <hverkuil-cisco@...all.nl>
To: Benjamin Gaignard <benjamin.gaignard@...labora.com>,
Tomasz Figa <tfiga@...omium.org>
Cc: mchehab@...nel.org, m.szyprowski@...sung.com, ming.qian@....com,
ezequiel@...guardiasur.com.ar, p.zabel@...gutronix.de,
gregkh@...uxfoundation.org, nicolas.dufresne@...labora.com,
linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
linux-rockchip@...ts.infradead.org, linux-staging@...ts.linux.dev,
kernel@...labora.com
Subject: Re: [PATCH v14 02/56] media: videobuf2: Rework offset 'cookie'
encoding pattern
On 08/11/2023 11:14, Benjamin Gaignard wrote:
>
> Le 08/11/2023 à 07:23, Tomasz Figa a écrit :
>> Hi Benjamin,
>>
>> On Tue, Oct 31, 2023 at 05:30:10PM +0100, Benjamin Gaignard wrote:
>>> Change how offset 'cookie' field value is computed to make possible
>>> to use more buffers.
>>> The maximum number of buffers depends of PAGE_SHIFT value and can
>>> go up to 0x7fff when PAGE_SHIFT = 12.
>>> With this encoding pattern we know the maximum number that a queue
>>> could store so we can check it at queue init time.
>>> It also make easier and faster to find buffer and plane from using
>>> the offset field.
>>> Change __find_plane_by_offset() prototype to return the video buffer
>>> itself rather than it index.
>>>
>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
>>> ---
>>> .../media/common/videobuf2/videobuf2-core.c | 73 +++++++++----------
>>> 1 file changed, 35 insertions(+), 38 deletions(-)
>>>
>> Thanks a lot for working on this series. Just one comment inline.
>>
>>> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
>>> index a5e57affeb30..09be8e026044 100644
>>> --- a/drivers/media/common/videobuf2/videobuf2-core.c
>>> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
>>> @@ -31,6 +31,11 @@
>>> #include <trace/events/vb2.h>
>>> +#define PLANE_INDEX_SHIFT (PAGE_SHIFT + 3)
>>> +#define PLANE_INDEX_MASK 0x7
>> Could we somehow ensure that it indeed matches VIDEO_MAX_PLANES?
>>
>> One thing that comes to my mind would be
>>
>> #define PLANE_INDEX_BITS 3
>> #define PLANE_INDEX_SHIFT (PAGE_SHIFT + PLANE_INDEX_BITS)
>> #define PLANE_INDEX_MASK BIT_MASK(PLANE_INDEX_BITS)
>>
>> BUILD_BUG_ON(BIT(PLANE_INDEX_BITS) != VIDEO_MAX_PLANES);
>>
>> Alternatively we could change the videodev2.h, so that we have
>>
>> #define VIDEO_MAX_PLANES_BITS 3
>> #define VIDEO_MAX_PLANES (1U < VIDEO_MAX_PLANES_BITS)
>>
>> and then we can just VIDEO_MAX_PLANES_BITS in our definitions in this file
>> and no checks would be necessary.
>
> I would prefer this solution.
> Hans should I do that in an other patch ?
I prefer to not make changes in videodev2.h, to be honest. I think it is fine to
just add a check in videobuf2-core.c.
Regards,
Hans
>
> Regards,
> Benjamin
>
>>
>> Best regards,
>> Tomasz
>>
>>> +#define MAX_BUFFER_INDEX BIT_MASK(30 - PLANE_INDEX_SHIFT)
>>> +#define BUFFER_INDEX_MASK (MAX_BUFFER_INDEX - 1)
>>> +
>>> static int debug;
>>> module_param(debug, int, 0644);
>>> @@ -358,21 +363,27 @@ static void __setup_offsets(struct vb2_buffer *vb)
>>> unsigned int plane;
>>> unsigned long offset = 0;
>>> - if (vb->index) {
>>> - struct vb2_buffer *prev = q->bufs[vb->index - 1];
>>> - struct vb2_plane *p = &prev->planes[prev->num_planes - 1];
>>> -
>>> - offset = PAGE_ALIGN(p->m.offset + p->length);
>>> - }
>>> + /*
>>> + * The offset "cookie" value has the following constraints:
>>> + * - a buffer can have up to 8 planes.
>>> + * - v4l2 mem2mem uses bit 30 to distinguish between
>>> + * OUTPUT (aka "source", bit 30 is 0) and
>>> + * CAPTURE (aka "destination", bit 30 is 1) buffers.
>>> + * - must be page aligned
>>> + * That led to this bit mapping when PAGE_SHIFT = 12:
>>> + * |30 |29 15|14 12|11 0|
>>> + * |DST_QUEUE_OFF_BASE|buffer index|plane index| 0 |
>>> + * where there are 15 bits to store the buffer index.
>>> + * Depending on PAGE_SHIFT value we can have fewer bits
>>> + * to store the buffer index.
>>> + */
>>> + offset = vb->index << PLANE_INDEX_SHIFT;
>>> for (plane = 0; plane < vb->num_planes; ++plane) {
>>> - vb->planes[plane].m.offset = offset;
>>> + vb->planes[plane].m.offset = offset + (plane << PAGE_SHIFT);
>>> dprintk(q, 3, "buffer %d, plane %d offset 0x%08lx\n",
>>> vb->index, plane, offset);
>>> -
>>> - offset += vb->planes[plane].length;
>>> - offset = PAGE_ALIGN(offset);
>>> }
>>> }
>>> @@ -2188,10 +2199,9 @@ EXPORT_SYMBOL_GPL(vb2_core_streamoff);
>>> * __find_plane_by_offset() - find plane associated with the given offset
>>> */
>>> static int __find_plane_by_offset(struct vb2_queue *q, unsigned long offset,
>>> - unsigned int *_buffer, unsigned int *_plane)
>>> + struct vb2_buffer **vb, unsigned int *plane)
>>> {
>>> - struct vb2_buffer *vb;
>>> - unsigned int buffer, plane;
>>> + unsigned int buffer;
>>> /*
>>> * Sanity checks to ensure the lock is held, MEMORY_MMAP is
>>> @@ -2209,24 +2219,15 @@ static int __find_plane_by_offset(struct vb2_queue *q, unsigned long offset,
>>> return -EBUSY;
>>> }
>>> - /*
>>> - * Go over all buffers and their planes, comparing the given offset
>>> - * with an offset assigned to each plane. If a match is found,
>>> - * return its buffer and plane numbers.
>>> - */
>>> - for (buffer = 0; buffer < q->num_buffers; ++buffer) {
>>> - vb = q->bufs[buffer];
>>> + /* Get buffer and plane from the offset */
>>> + buffer = (offset >> PLANE_INDEX_SHIFT) & BUFFER_INDEX_MASK;
>>> + *plane = (offset >> PAGE_SHIFT) & PLANE_INDEX_MASK;
>>> - for (plane = 0; plane < vb->num_planes; ++plane) {
>>> - if (vb->planes[plane].m.offset == offset) {
>>> - *_buffer = buffer;
>>> - *_plane = plane;
>>> - return 0;
>>> - }
>>> - }
>>> - }
>>> + if (buffer >= q->num_buffers || *plane >= q->bufs[buffer]->num_planes)
>>> + return -EINVAL;
>>> - return -EINVAL;
>>> + *vb = q->bufs[buffer];
>>> + return 0;
>>> }
>>> int vb2_core_expbuf(struct vb2_queue *q, int *fd, unsigned int type,
>>> @@ -2306,7 +2307,7 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma)
>>> {
>>> unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
>>> struct vb2_buffer *vb;
>>> - unsigned int buffer = 0, plane = 0;
>>> + unsigned int plane = 0;
>>> int ret;
>>> unsigned long length;
>>> @@ -2335,12 +2336,10 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma)
>>> * Find the plane corresponding to the offset passed by userspace. This
>>> * will return an error if not MEMORY_MMAP or file I/O is in progress.
>>> */
>>> - ret = __find_plane_by_offset(q, offset, &buffer, &plane);
>>> + ret = __find_plane_by_offset(q, offset, &vb, &plane);
>>> if (ret)
>>> goto unlock;
>>> - vb = q->bufs[buffer];
>>> -
>>> /*
>>> * MMAP requires page_aligned buffers.
>>> * The buffer length was page_aligned at __vb2_buf_mem_alloc(),
>>> @@ -2368,7 +2367,7 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma)
>>> if (ret)
>>> return ret;
>>> - dprintk(q, 3, "buffer %d, plane %d successfully mapped\n", buffer, plane);
>>> + dprintk(q, 3, "buffer %u, plane %d successfully mapped\n", vb->index, plane);
>>> return 0;
>>> }
>>> EXPORT_SYMBOL_GPL(vb2_mmap);
>>> @@ -2382,7 +2381,7 @@ unsigned long vb2_get_unmapped_area(struct vb2_queue *q,
>>> {
>>> unsigned long offset = pgoff << PAGE_SHIFT;
>>> struct vb2_buffer *vb;
>>> - unsigned int buffer, plane;
>>> + unsigned int plane;
>>> void *vaddr;
>>> int ret;
>>> @@ -2392,12 +2391,10 @@ unsigned long vb2_get_unmapped_area(struct vb2_queue *q,
>>> * Find the plane corresponding to the offset passed by userspace. This
>>> * will return an error if not MEMORY_MMAP or file I/O is in progress.
>>> */
>>> - ret = __find_plane_by_offset(q, offset, &buffer, &plane);
>>> + ret = __find_plane_by_offset(q, offset, &vb, &plane);
>>> if (ret)
>>> goto unlock;
>>> - vb = q->bufs[buffer];
>>> -
>>> vaddr = vb2_plane_vaddr(vb, plane);
>>> mutex_unlock(&q->mmap_lock);
>>> return vaddr ? (unsigned long)vaddr : -EINVAL;
>>> --
>>> 2.39.2
>>>
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