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From: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
To: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>
Cc: robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org,
	frowand.list-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
	devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	hch-jcswGhMUV9g@public.gmane.org,
	m.szyprowski-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org,
	stefan.wahren-eS4NqCHxEME@public.gmane.org,
	afaerber-l3A5Bk7waGM@public.gmane.org,
	hverkuil-qWit8jRvyhVmR6Xm/wNWPw@public.gmane.org,
	johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org
Subject: Re: [PATCH 2/2] of: Restrict DMA configuration
Date: Fri, 11 Aug 2017 20:01:06 +0200	[thread overview]
Message-ID: <20170811180106.GB1921@lst.de> (raw)
In-Reply-To: <82633e62b64e28dc18bc466319065b92faf2414f.1502468875.git.robin.murphy-5wv7dgnIgG8@public.gmane.org>

On Fri, Aug 11, 2017 at 05:29:57PM +0100, Robin Murphy wrote:
> The good news is that DT already gives us the ammunition to do the right
> thing - anything lacking a "dma-ranges" property should be considered
> not to have a mapping of DMA address space from its children to its
> parent, thus anything for which of_dma_get_range() does not succeed does
> not need DMA configuration.

That sounds like a good heuristic.

At least in theory apparently :(

> The bad news is that strictly enforcing that would likely break just
> about every FDT platform out there, since most authors have either not
> considered the property at all or have mistakenly assumed that omitting
> "dma-ranges" is equivalent to including the empty property. Thus we have
> little choice but to special-case platform, AMBA and PCI devices so they
> continue to receive configuration unconditionally as before. At least
> anything new will have to get it right in future...

That still sounds like a useful compromise.

>  	ret = of_dma_get_range(np, &dma_addr, &paddr, &size);
>  	if (ret < 0) {
> +		/*
> +		 * For legacy reasons, we have to assume some devices need
> +		 * DMA configuration regardless of whether "dma-ranges" is
> +		 * correctly specified or not.
> +		 */
> +		if (!dev_is_pci(dev) &&
> +#ifdef CONFIG_ARM_AMBA
> +		    dev->bus != &amba_bustype &&
> +#endif
> +		    dev->bus != &platform_bus_type)
> +			return ret == -ENODEV ? 0 : ret;
> +

It would be really nice to have dev_is_amba and dev_is_plaform helpers
to reduce the ifdef mess.

But it should be okay even without that cleanup.

> +	if (!size)
> +		size = max(dev->coherent_dma_mask, dev->coherent_dma_mask + 1);

I find this way to deal with an overflow really odd, but given that it's
just moved around I'm not going to complain.
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  parent reply	other threads:[~2017-08-11 18:01 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-11 16:29 [PATCH 1/2] of: Fix DMA mask generation Robin Murphy
2017-08-11 16:29 ` [PATCH 2/2] of: Restrict DMA configuration Robin Murphy
     [not found]   ` <82633e62b64e28dc18bc466319065b92faf2414f.1502468875.git.robin.murphy-5wv7dgnIgG8@public.gmane.org>
2017-08-11 18:01     ` Christoph Hellwig [this message]
2017-08-14 20:08     ` Rob Herring
     [not found]       ` <CAL_JsqKW7nhkCDu4eEDCgdC87b0MLH1UFO8LvaH22BcJMBsY7w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-15 10:18         ` Robin Murphy
     [not found]           ` <6819c6ae-e898-3293-d8b0-7a80108d7628-5wv7dgnIgG8@public.gmane.org>
2017-08-15 14:19             ` Rob Herring
2017-08-25 14:54               ` Christoph Hellwig
2017-08-11 17:56 ` [PATCH 1/2] of: Fix DMA mask generation Christoph Hellwig
     [not found] ` <0819179085df6c41c70e83a2c5c138b95c0386b3.1502468875.git.robin.murphy-5wv7dgnIgG8@public.gmane.org>
2017-08-14 21:09   ` Rob Herring
2017-08-17  8:24     ` Christoph Hellwig

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