linux-kernel - Re: [RFC PATCH] dma-mapping: create iommu mapping for newly allocated dma coherent mem

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Date:   Fri, 26 Apr 2019 17:13:30 +0200
From:   Christoph Hellwig <hch@....de>
To:     Laurentiu Tudor <laurentiu.tudor@....com>
Cc:     Christoph Hellwig <hch@....de>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Leo Li <leoyang.li@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] dma-mapping: create iommu mapping for newly
 allocated dma coherent mem

On Thu, Apr 25, 2019 at 11:30:54AM +0000, Laurentiu Tudor wrote:
> > I think the first step is to move the two USB controller that can only
> > DMA to their own BAR off the existing DMA coherent infrastructure.  The
> > controllers are already identified using the HCD_LOCAL_MEM flag, so we
> > just need to key off that in the hcd_buffer_* routines and call into a
> 
> So if HCD_LOCAL_MEM is set I should call into the gen_pool api instead 
> of existing dma_{alloc,free}_coherent().

Yes.

> > genalloc that has been fed using the bar, replacing the current
> > dma_declare_coherent usage.  Take a look at drivers/pci/p2pdma.c
> > for another example of allocating bits of a BAR using genalloc.
> 
> Where should I place the reference to the gen_pool? How does local_pool 
> in 'struct hcd_usb' sound?

Sounds fine to me, but in the end the usb maintainers will have
to decide.