Re: [PATCH 01/18] dma-direct: take dma-ranges/offsets into account in resource mapping

From: Christoph Hellwig <hch@lst.de>
To: Dave Stevenson <dave.stevenson@raspberrypi.com>
Cc: Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Florian Fainelli <florian.fainelli@broadcom.com>,
	Broadcom internal kernel review list
	<bcm-kernel-feedback-list@broadcom.com>,
	Ray Jui <rjui@broadcom.com>,
	Scott Branden <sbranden@broadcom.com>,
	Vinod Koul <vkoul@kernel.org>, Maxime Ripard <mripard@kernel.org>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Mark Brown <broonie@kernel.org>, Christoph Hellwig <hch@lst.de>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
	Vladimir Murzin <vladimir.murzin@arm.com>,
	Phil Elwell <phil@raspberrypi.com>,
	Stefan Wahren <wahrenst@gmx.net>,
	Serge Semin <Sergey.Semin@baikalelectronics.ru>,
	devicetree@vger.kernel.org, linux-rpi-kernel@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linux-mmc@vger.kernel.org,
	linux-spi@vger.kernel.org, iommu@lists.linux.dev,
	linux-sound@vger.kernel.org
Subject: Re: [PATCH 01/18] dma-direct: take dma-ranges/offsets into account in resource mapping
Date: Tue, 28 May 2024 08:33:32 +0200	[thread overview]
Message-ID: <20240528063332.GA30051@lst.de> (raw)
In-Reply-To: <20240524182702.1317935-2-dave.stevenson@raspberrypi.com>

On Fri, May 24, 2024 at 07:26:45PM +0100, Dave Stevenson wrote:
> From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> 
> A basic device-specific linear memory mapping was introduced back in
> commit ("dma: Take into account dma_pfn_offset") as a single-valued offset
> preserved in the device.dma_pfn_offset field, which was initialized for
> instance by means of the "dma-ranges" DT property. Afterwards the
> functionality was extended to support more than one device-specific region
> defined in the device.dma_range_map list of maps. But all of these
> improvements concerned a single pointer, page or sg DMA-mapping methods,
> while the system resource mapping function turned to miss the
> corresponding modification. Thus the dma_direct_map_resource() method now
> just casts the CPU physical address to the device DMA address with no
> dma-ranges-based mapping taking into account, which is obviously wrong.
> Let's fix it by using the phys_to_dma_direct() method to get the
> device-specific bus address from the passed memory resource for the case
> of the directly mapped DMA.

My memory is getting a little bad, but as dma_direct_map_resource is
mostly used for (non-PCIe) peer to peer transfers, any kind of mapping
from the host address should be excluded.

(dma_direct_map_resource in general is a horrible interface and I'd
prefer everyone to switch to the map_sg based P2P support, but we
have plenty of users for it unfortunately)