Re: [PATCH v2 01/11] asm-generic: add dma_zone_size

From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To: Catalin Marinas <catalin.marinas@arm.com>,
	Christoph Hellwig <hch@lst.de>
Cc: linux-arch@vger.kernel.org, devicetree@vger.kernel.org,
	f.fainelli@gmail.com, phill@raspberryi.org,
	Arnd Bergmann <arnd@arndb.de>,
	mbrugger@suse.com, marc.zyngier@arm.com, frowand.list@gmail.com,
	wahrenst@gmx.net, eric@anholt.net, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, iommu@lists.linux-foundation.org,
	robh+dt@kernel.org, linux-rpi-kernel@lists.infradead.org,
	Robin Murphy <robin.murphy@arm.com>,
	linux-riscv@lists.infradead.org, will@kernel.org,
	akpm@linux-foundation.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 01/11] asm-generic: add dma_zone_size
Date: Fri, 30 Aug 2019 19:24:25 +0200	[thread overview]
Message-ID: <bdeda2206b751a1c6a8d2e0732186792282633c6.camel@suse.de> (raw)
In-Reply-To: <20190830144536.GJ36992@arrakis.emea.arm.com>

[-- Attachment #1.1: Type: text/plain, Size: 2088 bytes --]

On Fri, 2019-08-30 at 15:45 +0100, Catalin Marinas wrote:
> On Mon, Aug 26, 2019 at 03:46:52PM +0200, Nicolas Saenz Julienne wrote:
> > On Mon, 2019-08-26 at 09:09 +0200, Christoph Hellwig wrote:
> > > On Tue, Aug 20, 2019 at 04:58:09PM +0200, Nicolas Saenz Julienne wrote:
> > > > Some architectures have platform specific DMA addressing limitations.
> > > > This will allow for hardware description code to provide the constraints
> > > > in a generic manner, so as for arch code to properly setup it's memory
> > > > zones and DMA mask.
> > > 
> > > I know this just spreads the arm code, but I still kinda hate it.
> > 
> > Rob's main concern was finding a way to pass the constraint from HW
> > definition
> > to arch without widening fdt's architecture specific function surface. I'd
> > say
> > it's fair to argue that having a generic mechanism makes sense as it'll now
> > traverse multiple archs and subsystems.
> > 
> > I get adding globals like this is not very appealing, yet I went with it as
> > it
> > was the easier to integrate with arm's code. Any alternative suggestions?
> 
> In some discussion with Robin, since it's just RPi4 that we are aware of
> having such requirement on arm64, he suggested that we have a permanent
> ZONE_DMA on arm64 with a default size of 1GB. It should cover all arm64
> SoCs we know of without breaking the single Image binary. The arch/arm
> can use its current mach-* support.
> 
> I may like this more than the proposed early_init_dt_get_dma_zone_size()
> here which checks for specific SoCs (my preferred way was to build the
> mask from all buses described in DT but I hadn't realised the
> complications).

Hi Catalin, thanks for giving it a thought.

I'll be happy to implement it that way. I agree it's a good compromise.

@Christoph, do you still want the patch where I create 'zone_dma_bits'? With a
hardcoded ZONE_DMA it's not absolutely necessary. Though I remember you said it
was a first step towards being able to initialize dma-direct's min_mask in
meminit.

Regards,
Nicolas

[-- Attachment #1.2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

[-- Attachment #2: Type: text/plain, Size: 156 bytes --]

_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu