Re: [PATCH v3 2/4] videobuf2-dma-streaming: new videobuf2 memory allocator

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em 24-09-2012 09:44, Marek Szyprowski escreveu:
> Hello,
>
> On Monday, September 24, 2012 12:59 PM Federico Vaga wrote:
>
>> The DMA streaming allocator is similar to the DMA contig but it use the
>> DMA streaming interface (dma_map_single, dma_unmap_single). The
>> allocator allocates buffers and immediately map the memory for DMA
>> transfer. For each buffer prepare/finish it does a DMA synchronization.

Hmm.. the explanation didn't convince me, e. g.:
	1) why is it needed;
	2) why vb2-dma-config can't be patched to use dma_map_single
(eventually using a different vb2_io_modes bit?);
	3) what are the usecases for it.

Could you please detail it? Without that, one that would be needing to
write a driver will have serious doubts about what would be the right
driver for its usage. Also, please document it at the driver itself.

Thanks!
Mauro

>>
>> Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
>
> Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
>
>> ---
>>   drivers/media/v4l2-core/Kconfig                   |   5 +
>>   drivers/media/v4l2-core/Makefile                  |   1 +
>>   drivers/media/v4l2-core/videobuf2-dma-streaming.c | 205 ++++++++++++++++++++++
>>   include/media/videobuf2-dma-streaming.h           |  32 ++++
>>   4 file modificati, 243 inserzioni(+)
>>   create mode 100644 drivers/media/v4l2-core/videobuf2-dma-streaming.c
>>   create mode 100644 include/media/videobuf2-dma-streaming.h
>>
>> diff --git a/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-core/Kconfig
>> index 0c54e19..60548a7 100644
>> --- a/drivers/media/v4l2-core/Kconfig
>> +++ b/drivers/media/v4l2-core/Kconfig
>> @@ -79,3 +79,8 @@ config VIDEOBUF2_DMA_SG
>>   	#depends on HAS_DMA
>>   	select VIDEOBUF2_CORE
>>   	select VIDEOBUF2_MEMOPS
>> +
>> +config VIDEOBUF2_DMA_STREAMING
>> +	select VIDEOBUF2_CORE
>> +	select VIDEOBUF2_MEMOPS
>> +	tristate
>> diff --git a/drivers/media/v4l2-core/Makefile b/drivers/media/v4l2-core/Makefile
>> index c2d61d4..0b2756f 100644
>> --- a/drivers/media/v4l2-core/Makefile
>> +++ b/drivers/media/v4l2-core/Makefile
>> @@ -28,6 +28,7 @@ obj-$(CONFIG_VIDEOBUF2_MEMOPS) += videobuf2-memops.o
>>   obj-$(CONFIG_VIDEOBUF2_VMALLOC) += videobuf2-vmalloc.o
>>   obj-$(CONFIG_VIDEOBUF2_DMA_CONTIG) += videobuf2-dma-contig.o
>>   obj-$(CONFIG_VIDEOBUF2_DMA_SG) += videobuf2-dma-sg.o
>> +obj-$(CONFIG_VIDEOBUF2_DMA_STREAMING) += videobuf2-dma-streaming.o
>>
>>   ccflags-y += -I$(srctree)/drivers/media/dvb-core
>>   ccflags-y += -I$(srctree)/drivers/media/dvb-frontends
>> diff --git a/drivers/media/v4l2-core/videobuf2-dma-streaming.c b/drivers/media/v4l2-
>> core/videobuf2-dma-streaming.c
>> new file mode 100644
>> index 0000000..c839e05
>> --- /dev/null
>> +++ b/drivers/media/v4l2-core/videobuf2-dma-streaming.c
>> @@ -0,0 +1,205 @@
>> +/*
>> + * videobuf2-dma-streaming.c - DMA streaming memory allocator for videobuf2
>> + *
>> + * Copyright (C) 2012 Federico Vaga <federico.vaga@gmail.com>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + */
>> +
>> +#include <linux/module.h>
>> +#include <linux/slab.h>
>> +#include <linux/pagemap.h>
>> +#include <linux/dma-mapping.h>
>> +
>> +#include <media/videobuf2-core.h>
>> +#include <media/videobuf2-dma-streaming.h>
>> +#include <media/videobuf2-memops.h>
>> +
>> +struct vb2_streaming_conf {
>> +	struct device			*dev;
>> +};
>> +struct vb2_streaming_buf {
>> +	struct vb2_streaming_conf	*conf;
>> +	void				*vaddr;
>> +
>> +	dma_addr_t			dma_handle;
>> +
>> +	unsigned long			size;
>> +	struct vm_area_struct		*vma;
>> +
>> +	atomic_t			refcount;
>> +	struct vb2_vmarea_handler	handler;
>> +};
>> +
>> +static void vb2_dma_streaming_put(void *buf_priv)
>> +{
>> +	struct vb2_streaming_buf *buf = buf_priv;
>> +
>> +	if (atomic_dec_and_test(&buf->refcount)) {
>> +		dma_unmap_single(buf->conf->dev, buf->dma_handle, buf->size,
>> +				 DMA_FROM_DEVICE);
>> +		free_pages_exact(buf->vaddr, buf->size);
>> +		kfree(buf);
>> +	}
>> +
>> +}
>> +
>> +static void *vb2_dma_streaming_alloc(void *alloc_ctx, unsigned long size)
>> +{
>> +	struct vb2_streaming_conf *conf = alloc_ctx;
>> +	struct vb2_streaming_buf *buf;
>> +	int err;
>> +
>> +	buf = kzalloc(sizeof(struct vb2_streaming_buf), GFP_KERNEL);
>> +	if (!buf)
>> +		return ERR_PTR(-ENOMEM);
>> +	buf->vaddr = alloc_pages_exact(size, GFP_KERNEL | GFP_DMA);
>> +	if (!buf->vaddr) {
>> +		err = -ENOMEM;
>> +		goto out;
>> +	}
>> +	buf->dma_handle = dma_map_single(conf->dev, buf->vaddr, size,
>> +					 DMA_FROM_DEVICE);
>> +	err = dma_mapping_error(conf->dev, buf->dma_handle);
>> +	if (err) {
>> +		dev_err(conf->dev, "dma_map_single failed\n");
>> +
>> +		free_pages_exact(buf->vaddr, size);
>> +		buf->vaddr = NULL;
>> +		goto out_pages;
>> +	}
>> +	buf->conf = conf;
>> +	buf->size = size;
>> +	buf->handler.refcount = &buf->refcount;
>> +	buf->handler.put = vb2_dma_streaming_put;
>> +	buf->handler.arg = buf;
>> +
>> +	atomic_inc(&buf->refcount);
>> +	return buf;
>> +
>> +out_pages:
>> +	free_pages_exact(buf->vaddr, buf->size);
>> +out:
>> +	kfree(buf);
>> +	return ERR_PTR(err);
>> +}
>> +
>> +static void *vb2_dma_streaming_cookie(void *buf_priv)
>> +{
>> +	struct vb2_streaming_buf *buf = buf_priv;
>> +
>> +	return &buf->dma_handle;
>> +}
>> +
>> +static void *vb2_dma_streaming_vaddr(void *buf_priv)
>> +{
>> +	struct vb2_streaming_buf *buf = buf_priv;
>> +
>> +	if (!buf)
>> +		return NULL;
>> +	return buf->vaddr;
>> +}
>> +
>> +static unsigned int vb2_dma_streaming_num_users(void *buf_priv)
>> +{
>> +	struct vb2_streaming_buf *buf = buf_priv;
>> +
>> +	return atomic_read(&buf->refcount);
>> +}
>> +
>> +static int vb2_dma_streaming_mmap(void *buf_priv, struct vm_area_struct *vma)
>> +{
>> +	struct vb2_streaming_buf *buf = buf_priv;
>> +	unsigned long pos, start = vma->vm_start;
>> +	unsigned long size;
>> +	struct page *page;
>> +	int err;
>> +
>> +	/* Try to remap memory */
>> +	size = vma->vm_end - vma->vm_start;
>> +	size = (size < buf->size) ? size : buf->size;
>> +	pos = (unsigned long)buf->vaddr;
>> +
>> +	while (size > 0) {
>> +		page = virt_to_page((void *)pos);
>> +		if (!page) {
>> +			dev_err(buf->conf->dev, "mmap: virt_to_page failed\n");
>> +			return -ENOMEM;
>> +		}
>> +		err = vm_insert_page(vma, start, page);
>> +		if (err) {
>> +			dev_err(buf->conf->dev, "mmap: insert failed %d\n", err);
>> +			return -ENOMEM;
>> +		}
>> +		start += PAGE_SIZE;
>> +		pos += PAGE_SIZE;
>> +
>> +		if (size > PAGE_SIZE)
>> +			size -= PAGE_SIZE;
>> +		else
>> +			size = 0;
>> +	}
>> +
>> +
>> +	vma->vm_ops = &vb2_common_vm_ops;
>> +	vma->vm_flags |= VM_DONTEXPAND;
>> +	vma->vm_private_data = &buf->handler;
>> +
>> +	vma->vm_ops->open(vma);
>> +
>> +	return 0;
>> +}
>> +
>> +static void vb2_dma_streaming_prepare(void *buf_priv)
>> +{
>> +	struct vb2_streaming_buf *buf = buf_priv;
>> +
>> +	dma_sync_single_for_device(buf->conf->dev, buf->dma_handle,
>> +				   buf->size, DMA_FROM_DEVICE);
>> +}
>> +
>> +static void vb2_dma_streaming_finish(void *buf_priv)
>> +{
>> +	struct vb2_streaming_buf *buf = buf_priv;
>> +
>> +	dma_sync_single_for_cpu(buf->conf->dev, buf->dma_handle,
>> +				buf->size, DMA_FROM_DEVICE);
>> +}
>> +
>> +const struct vb2_mem_ops vb2_dma_streaming_memops = {
>> +	.alloc		= vb2_dma_streaming_alloc,
>> +	.put		= vb2_dma_streaming_put,
>> +	.cookie		= vb2_dma_streaming_cookie,
>> +	.vaddr		= vb2_dma_streaming_vaddr,
>> +	.mmap		= vb2_dma_streaming_mmap,
>> +	.num_users	= vb2_dma_streaming_num_users,
>> +	.prepare	= vb2_dma_streaming_prepare,
>> +	.finish		= vb2_dma_streaming_finish,
>> +};
>> +EXPORT_SYMBOL_GPL(vb2_dma_streaming_memops);
>> +
>> +void *vb2_dma_streaming_init_ctx(struct device *dev)
>> +{
>> +	struct vb2_streaming_conf *conf;
>> +
>> +	conf = kmalloc(sizeof(struct vb2_streaming_conf), GFP_KERNEL);
>> +	if (!conf)
>> +		return ERR_PTR(-ENOMEM);
>> +
>> +	conf->dev = dev;
>> +
>> +	return conf;
>> +}
>> +EXPORT_SYMBOL_GPL(vb2_dma_streaming_init_ctx);
>> +
>> +void vb2_dma_streaming_cleanup_ctx(void *alloc_ctx)
>> +{
>> +	kfree(alloc_ctx);
>> +}
>> +EXPORT_SYMBOL_GPL(vb2_dma_streaming_cleanup_ctx);
>> +
>> +MODULE_DESCRIPTION("DMA-streaming memory allocator for videobuf2");
>> +MODULE_AUTHOR("Federico Vaga <federico.vaga@gmail.com>");
>> +MODULE_LICENSE("GPL v2");
>> diff --git a/include/media/videobuf2-dma-streaming.h b/include/media/videobuf2-dma-streaming.h
>> new file mode 100644
>> index 0000000..2a62d93
>> --- /dev/null
>> +++ b/include/media/videobuf2-dma-streaming.h
>> @@ -0,0 +1,32 @@
>> +/*
>> + * videobuf2-dma-streaming.h - DMA streaming memory allocator for videobuf2
>> + *
>> + * Copyright (C) 2012 Federico Vaga
>> + *
>> + * Author: Federico Vaga <federico.vaga@gmail.com>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License as published by
>> + * the Free Software Foundation.
>> + */
>> +
>> +#ifndef _MEDIA_VIDEOBUF2_DMA_STREAMING_H
>> +#define _MEDIA_VIDEOBUF2_DMA_STREAMING_H
>> +
>> +#include <media/videobuf2-core.h>
>> +#include <linux/dma-mapping.h>
>> +
>> +void *vb2_dma_streaming_init_ctx(struct device *dev);
>> +void vb2_dma_streaming_cleanup_ctx(void *alloc_ctx);
>> +
>> +extern const struct vb2_mem_ops vb2_dma_streaming_memops;
>> +
>> +static inline dma_addr_t
>> +vb2_dma_streaming_plane_paddr(struct vb2_buffer *vb, unsigned int plane_no)
>> +{
>> +	dma_addr_t *dma_addr = vb2_plane_cookie(vb, plane_no);
>> +
>> +	return *dma_addr;
>> +}
>> +
>> +#endif
>> --
>> 1.7.11.4
>
> Best regards
>