RE: UBIFS with dma on 4.6 kernel is not working

[Naga Sureshkumar Relli]

Hi,

Thanks everybody for your valuable information.

I am not aware of all these dma related APIs but where to handle these dma stuff?
Is it in UBI/UBIFS(at the time of vmalloc allocations)? Or in controller driver?

And also is there a way to know the memory allocated using vmalloc is contiguous or not?
Based on that I can switch my driver to work in dma or non-dma mode for ubifs use.

Thanks,
Naga Sureshkumar Relli

-----Original Message-----
From: Christoph Hellwig [mailto:hch@xxxxxxxxxxxxx] 
Sent: Friday, October 21, 2016 6:45 PM
To: Richard Weinberger <richard@xxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>; Naga Sureshkumar Relli <nagasure@xxxxxxxxxx>; dwmw2@xxxxxxxxxxxxx; computersforpeace@xxxxxxxxx; dedekind1@xxxxxxxxx; adrian.hunter@xxxxxxxxx; michal.simek@xxxxxxxxxx; Punnaiah Choudary Kalluri <punnaia@xxxxxxxxxx>; linux-mtd@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx>
Subject: Re: UBIFS with dma on 4.6 kernel is not working

On Fri, Oct 21, 2016 at 03:07:57PM +0200, Richard Weinberger wrote:
> Hmm, thought this is still problematic on VIVT architectures.
> Boris tried to provide a solution for that some time ago:
> http://www.spinics.net/lists/arm-kernel/msg494025.html

Things have been working fine for approx 10 years when using flush_kernel_vmap_range before doing I/O using the physical addresses and then invalidate_kernel_vmap_range when completing the I/O and going back to using the virtual mapping for XFS.

Of course all this assumes at least the higher level that did the vm_map_ram operation knows about this dance between virtually mapped and physiscal addresses.