RE: [PATCH 2/3] [media] videobuf2-dma-streaming: new videobuf2 memoryallocator

[Marek Szyprowski]

Hello,

I'm really sorry for a late reply, but I was a bit busy with other stuff.

On Tuesday, July 31, 2012 10:17 PM Federico Vaga wrote:

> Signed-off-by: Federico Vaga <federico.vaga@xxxxxxxxx>
> ---
>  drivers/media/video/Kconfig                   |   6 +-
>  drivers/media/video/Makefile                  |   1 +
>  drivers/media/video/videobuf2-dma-streaming.c | 187 ++++++++++++++++++++++++++
>  include/media/videobuf2-dma-streaming.h       |  24 ++++
>  4 file modificati, 217 inserzioni(+). 1 rimozione(-)
>  create mode 100644 drivers/media/video/videobuf2-dma-streaming.c
>  create mode 100644 include/media/videobuf2-dma-streaming.h
> 
> diff --git a/drivers/media/video/Kconfig b/drivers/media/video/Kconfig
> index be6d718..6c60b59 100644
> --- a/drivers/media/video/Kconfig
> +++ b/drivers/media/video/Kconfig
> @@ -59,6 +59,10 @@ config VIDEOBUF2_DMA_NC
>  	select VIDEOBUF2_CORE
>  	select VIDEOBUF2_MEMOPS
>  	tristate
> +config VIDEOBUF2_DMA_STREAMING
> +	select VIDEOBUF2_CORE
> +	select VIDEOBUF2_MEMOPS
> +	tristate
> 
>  config VIDEOBUF2_VMALLOC
>  	select VIDEOBUF2_CORE
> @@ -844,7 +848,7 @@ config STA2X11_VIP
>  	tristate "STA2X11 VIP Video For Linux"
>  	depends on STA2X11
>  	select VIDEO_ADV7180 if VIDEO_HELPER_CHIPS_AUTO
> -	select VIDEOBUF_DMA_CONTIG
> +	select VIDEOBUF2_DMA_STREAMING

This doesn't look like a part of this part.

>  	depends on PCI && VIDEO_V4L2 && VIRT_TO_BUS
>  	help
>  	  Say Y for support for STA2X11 VIP (Video Input Port) capture
> diff --git a/drivers/media/video/Makefile b/drivers/media/video/Makefile
> index 30234af..c1a08b9e 100644
> --- a/drivers/media/video/Makefile
> +++ b/drivers/media/video/Makefile
> @@ -140,6 +140,7 @@ 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_NC)		+= videobuf2-dma-nc.o
> +obj-$(CONFIG_VIDEOBUF2_DMA_STREAMING)	+= videobuf2-dma-streaming.o
> 
>  obj-$(CONFIG_V4L2_MEM2MEM_DEV) += v4l2-mem2mem.o
> 
> diff --git a/drivers/media/video/videobuf2-dma-streaming.c b/drivers/media/video/videobuf2-
> dma-streaming.c
> new file mode 100644
> index 0000000..d96d3d9
> --- /dev/null
> +++ b/drivers/media/video/videobuf2-dma-streaming.c
> @@ -0,0 +1,187 @@
> +/*
> + * videobuf2-dma-streaming.c - DMA streaming memory allocator for videobuf2
> + *
> + * Copyright (C) 2012 Federico Vaga <federico.vaga@xxxxxxxxx>
> + * *
> + * 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 *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 (void *)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;
> +}
> +
> +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,
> +};
> +EXPORT_SYMBOL_GPL(vb2_dma_streaming_memops);
> +
> +void *vb2_dma_streaming_init_ctx(struct device *dev)
> +{
> +	struct vb2_streaming_conf *conf;
> +
> +	conf = kmalloc(sizeof *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@xxxxxxxxx>");
> +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..89cbd06
> --- /dev/null
> +++ b/include/media/videobuf2-dma-streaming.h
> @@ -0,0 +1,24 @@
> +/*
> + * videobuf2-dma-streaming.h - DMA steaming memory allocator for videobuf2
> + *
> + * Copyright (C) 2012 Federico Vaga
> + *
> + * Author: Federico Vaga <federico.vaga@xxxxxxxxx>
> + *
> + * 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;
> +
> +#endif
> --
> 1.7.11.2

I'm aware of the fact that some system might require such method of memory allocation.
I don't want to delay merging it. I hope that one day it will be finally possible to
use dma_alloc_attrs() from dma-mapping subsystem for this purpose and extended 
videobuf2-dma-contig will handle it.

Getting back to your patch - in your approach cpu cache handling is missing. I suspect
that it worked fine only because it has been tested on some simple platform without
any cpu caches (or with very small ones). Please check the following thread: 
http://www.spinics.net/lists/linux-media/msg51768.html where Tomasz has posted his 
ongoing effort on updating and extending videobuf2 and dma-contig allocator. 
Especially the patch http://www.spinics.net/lists/linux-media/msg51776.html will be
interesting for you, because cpu cache synchronization (dma_sync_single_for_device /
dma_sync_single_for_cpu) should be called from prepare/finish callbacks.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center


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