Re: [PATCH] media: vimc: Add support for contiguous DMA buffers

[Dafna Hirschfeld <dafna.hirschfeld@collabora.com>]

On 30.07.21 15:11, Laurent Pinchart wrote:
> Hi Dafna,
> 
> On Fri, Jul 30, 2021 at 02:35:20PM +0200, Dafna Hirschfeld wrote:
>> On 30.07.21 02:19, Laurent Pinchart wrote:
>>> The vimc driver is used for testing purpose, and some test use cases
>>> involve sharing buffers with a consumer device. Consumers often require
>>> DMA contiguous memory, which vimc doesn't currently support. This leads
>>> in the best case to usage of bounce buffers, which is very slow, and in
>>> the worst case in a complete failure.
>>>
>>> Add support for the dma-contig allocator in vimc to support those use
>>> cases properly. The allocator is selected through a new "allocator"
>>> module parameter, which defaults to vmalloc.
>>>
>>> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
>>> ---
>>>    drivers/media/test-drivers/vimc/vimc-capture.c |  9 +++++++--
>>>    drivers/media/test-drivers/vimc/vimc-common.h  |  2 ++
>>>    drivers/media/test-drivers/vimc/vimc-core.c    | 10 ++++++++++
>>>    3 files changed, 19 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/media/test-drivers/vimc/vimc-capture.c b/drivers/media/test-drivers/vimc/vimc-capture.c
>>> index 5e9fd902cd37..92b69a6529fb 100644
>>> --- a/drivers/media/test-drivers/vimc/vimc-capture.c
>>> +++ b/drivers/media/test-drivers/vimc/vimc-capture.c
>>> @@ -7,6 +7,7 @@
>>>    
>>>    #include <media/v4l2-ioctl.h>
>>>    #include <media/videobuf2-core.h>
>>> +#include <media/videobuf2-dma-contig.h>
>>>    #include <media/videobuf2-vmalloc.h>
>>>    
>>>    #include "vimc-common.h"
>>> @@ -423,14 +424,18 @@ static struct vimc_ent_device *vimc_cap_add(struct vimc_device *vimc,
>>>    	/* Initialize the vb2 queue */
>>>    	q = &vcap->queue;
>>>    	q->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
>>> -	q->io_modes = VB2_MMAP | VB2_DMABUF | VB2_USERPTR;
>>> +	q->io_modes = VB2_MMAP | VB2_DMABUF;
>>
>> maybe to be on the safe side VB2_DMABUF should be set only if vimc_allocator==1 ?
> 
> Why so ? vb2-vmalloc can import dma-bufs.

oh, I meant that exporting should not be supported.
I see that vimc set ".vidioc_expbuf = vb2_ioctl_expbuf", maybe remove that if allocator is vmalloc?

Thanks,
Dafna

> 
>>> +	if (vimc_allocator != 1)
>>
>> maybe define a macro instead of `1` ?
> 
> Good idea.
> 
>>> +		q->io_modes |= VB2_USERPTR;
>>>    	q->drv_priv = vcap;
>>>    	q->buf_struct_size = sizeof(struct vimc_cap_buffer);
>>>    	q->ops = &vimc_cap_qops;
>>> -	q->mem_ops = &vb2_vmalloc_memops;
>>> +	q->mem_ops = vimc_allocator == 1
>>> +		   ? &vb2_dma_contig_memops : &vb2_vmalloc_memops;
>>>    	q->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
>>>    	q->min_buffers_needed = 2;
>>>    	q->lock = &vcap->lock;
>>> +	q->dev = v4l2_dev->dev;
>>>    
>>>    	ret = vb2_queue_init(q);
>>>    	if (ret) {
>>> diff --git a/drivers/media/test-drivers/vimc/vimc-common.h b/drivers/media/test-drivers/vimc/vimc-common.h
>>> index a289434e75ba..b77939123501 100644
>>> --- a/drivers/media/test-drivers/vimc/vimc-common.h
>>> +++ b/drivers/media/test-drivers/vimc/vimc-common.h
>>> @@ -35,6 +35,8 @@
>>>    
>>>    #define VIMC_PIX_FMT_MAX_CODES 8
>>>    
>>> +extern unsigned int vimc_allocator;
>>> +
>>>    /**
>>>     * vimc_colorimetry_clamp - Adjust colorimetry parameters
>>>     *
>>> diff --git a/drivers/media/test-drivers/vimc/vimc-core.c b/drivers/media/test-drivers/vimc/vimc-core.c
>>> index 4b0ae6f51d76..7badcecb7aed 100644
>>> --- a/drivers/media/test-drivers/vimc/vimc-core.c
>>> +++ b/drivers/media/test-drivers/vimc/vimc-core.c
>>> @@ -5,6 +5,7 @@
>>>     * Copyright (C) 2015-2017 Helen Koike <helen.fornazier@gmail.com>
>>>     */
>>>    
>>> +#include <linux/dma-mapping.h>
>>>    #include <linux/font.h>
>>>    #include <linux/init.h>
>>>    #include <linux/module.h>
>>> @@ -15,6 +16,12 @@
>>>    
>>>    #include "vimc-common.h"
>>>    
>>> +unsigned int vimc_allocator;
>>> +module_param_named(allocator, vimc_allocator, uint, 0444);
>>> +MODULE_PARM_DESC(allocator, " memory allocator selection, default is 0.\n"
>>> +			     "\t\t    0 == vmalloc\n"
>>> +			     "\t\t    1 == dma-contig");
>>> +
>>
>> There is a section 'Module options' in vimc.rst. So a doc should be added there.
> 
> OK, I'll update that.
> 
>>>    #define VIMC_MDEV_MODEL_NAME "VIMC MDEV"
>>>    
>>>    #define VIMC_ENT_LINK(src, srcpad, sink, sinkpad, link_flags) {	\
>>> @@ -278,6 +285,9 @@ static int vimc_probe(struct platform_device *pdev)
>>>    
>>>    	tpg_set_font(font->data);
>>>    
>>> +	if (vimc_allocator == 1)
>>> +		dma_coerce_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
>>> +
>>>    	vimc = kzalloc(sizeof(*vimc), GFP_KERNEL);
>>>    	if (!vimc)
>>>    		return -ENOMEM;
>>>
>