linux-kernel - Re: [PATCH 03/14] x86: use dma-direct

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Date:   Thu, 15 Mar 2018 13:53:52 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Christoph Hellwig <hch@....de>
cc:     x86@...nel.org, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Muli Ben-Yehuda <mulix@...ix.org>,
        Jon Mason <jdmason@...zu.us>, Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/14] x86: use dma-direct

On Thu, 15 Mar 2018, Christoph Hellwig wrote:

> On Thu, Mar 15, 2018 at 09:56:13AM +0100, Thomas Gleixner wrote:
> > On Wed, 14 Mar 2018, Christoph Hellwig wrote:
> > 
> > > The generic dma-direct implementation is now functionally equivalent to
> > > the x86 nommu dma_map implementation, so switch over to using it.
> > 
> > Can you please convert the various drivers first and then remove the
> > unused code?
> 
> Which various drivers?
> 
> > > Note that the various iommu drivers are switched from x86_dma_supported

The various iommu drivers ....

> > > to dma_direct_supported to provide identical functionality, although the
> > > checks looks fairly questionable for at least some of them.
> > 
> > Can you please elaborate? From the above it's not clear which checks you
> > are referring to. If you convert these drivers seperately then explicit
> > information about your concerns wants to be in the changelogs.
> 
> This bit:
> 
> 	/* Copied from i386. Doesn't make much sense, because it will
> 	   only work for pci_alloc_coherent.
> 	   The caller just has to use GFP_DMA in this case. */
> 	if (mask < DMA_BIT_MASK(24))
> 		return 0;
> 
> in x86_dma_supported, or the equivalent bit in dma_direct_supported.
> Kept for bug to bug compatibility, but I guess I should reword or
> just drop the changelog bit іf it causes confusion.

Reword please.

Thanks,

	tglx