Em 27-09-2011 05:23, Marek Szyprowski escreveu: > Hello, > > On Monday, September 26, 2011 3:30 PM Mauro Carvalho Chehab wrote: > >> Em 26-09-2011 08:21, Marek Szyprowski escreveu: >>> Hello, >>> >>> On Monday, September 26, 2011 1:14 PM Mauro Carvalho Chehab wrote: >>> >>>>> Scott Jiang (1): >>>>> vb2: add vb2_get_unmapped_area in vb2 core >>>> >>>>> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h >>>>> index ea55c08..977410b 100644 >>>>> --- a/include/media/videobuf2-core.h >>>>> +++ b/include/media/videobuf2-core.h >>>>> @@ -309,6 +309,13 @@ int vb2_streamon(struct vb2_queue *q, enum v4l2_buf_type type); >>>>> int vb2_streamoff(struct vb2_queue *q, enum v4l2_buf_type type); >>>>> >>>>> int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma); >>>>> +#ifndef CONFIG_MMU >>>>> +unsigned long vb2_get_unmapped_area(struct vb2_queue *q, >>>>> + unsigned long addr, >>>>> + unsigned long len, >>>>> + unsigned long pgoff, >>>>> + unsigned long flags); >>>>> +#endif >>>>> unsigned int vb2_poll(struct vb2_queue *q, struct file *file, poll_table *wait); >>>>> size_t vb2_read(struct vb2_queue *q, char __user *data, size_t count, >>>>> loff_t *ppos, int nonblock); >>>> >>>> This sounds me like a hack, as it is passing the problem of working with a non-mmu >>>> capable hardware to the driver, inserting architecture-dependent bits on them. >>>> >>>> The proper way to do it is to provide a vb2 core support to handle the non-mmu case >>>> inside it. >>> >>> This is exactly what this patch does - it provides generic vb2 implementation for >>> fops->get_unmapped_area callback which any vb2 ready driver can use. This operation >>> is used only on NON-MMU systems. Please check drivers/media/video/v4l2-dev.c file and >>> the implementation of get_unmapped_area there. Similar code is used by uvc driver. >> >> At least there, there is a: >> #ifdef CONFIG_MMU >> #define v4l2_get_unmapped_area NULL >> #else >> ... >> #endif >> >> block, so, in thesis, a driver can be written to support both cases without inserting >> #ifdefs inside it. > > videobuf2 functions are not meant to be used as direct callbacks in fops so defining it > as NULL makes no sense at all. > >> Ideally, I would prefer if all those iommu-specific calls would be inside the core. >> A driver should not need to do anything special in order to support a different >> (sub)architecture. > > It is not about IOMMU at all. Some (embedded) systems don't have MMU at all. Drivers on > such systems cannot do regular mmap operation. Instead it is emulated with > get_unmapped_area fops callback and some (u)libC magic. This patch just provides > vb2_get_unmapped_area function. Drivers have to call it from their respective > my_driver_get_unmapped_area() function provided in its fops. Implementing it makes > sense only on NO-MMU systems. I really see no other way of dealing with this. Ok. Feel free to add this patch again on a next request. Thanks, Mauro > > Best regards -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
