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From: Baruch Siach <baruch@tkos.co.il>
To: "Christoph Lameter (Ampere)" <cl@linux.com>
Cc: "Christoph Hellwig" <hch@lst.de>,
	"Marek Szyprowski" <m.szyprowski@samsung.com>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Frank Rowand" <frowand.list@gmail.com>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Will Deacon" <will@kernel.org>,
	"Robin Murphy" <robin.murphy@arm.com>,
	iommu@lists.linux.dev, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, "Petr Tesařík" <petr@tesarici.cz>,
	"Ramon Fried" <ramon@neureality.ai>
Subject: Re: [PATCH RFC 1/4] of: get dma area lower limit
Date: Thu, 18 Jan 2024 12:59:58 +0200	[thread overview]
Message-ID: <87cytyx5gf.fsf@tarshish> (raw)
In-Reply-To: <30d81f73-e27e-6cc4-5458-686e3ddd2e5c@linux.com>

Hi Christoph

On Wed, Jan 17 2024, Christoph Lameter (Ampere) wrote:
> On Wed, 27 Dec 2023, Baruch Siach wrote:
>> of_dma_get_max_cpu_address() returns the highest CPU address that
>> devices can use for DMA. The implicit assumption is that all CPU
>> addresses below that limit are suitable for DMA. However the
>> 'dma-ranges' property this code uses also encodes a lower limit for DMA
>> that is potentially non zero.
>
> All of memory can be used for DMA by default (==ZONE_NORMAL). ZONE_DMA defines
> a special range for devices that are unable to perform DMA to all of
> memory. Usually due to the lack of address bit support.
>
> So I guess that the platform in question here has as a general limit as to
> what address spaces I/O devices can do DMA to?

DMA to/from devices in bus with 'dma-ranges' property is limited to
address space described in 'dma-ranges'. The arm64 platform currently
uses 'dma-ranges' as a hint to set ZONE_DMA limits globally. This series
is meant to make ZONE_DMA limits adjustment code work better for
platforms where the lower DMA limit is above 4GB. This commit adds the
ability to extract the lower limit from 'dma-ranges'.

baruch

-- 
                                                     ~. .~   Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
   - baruch@tkos.co.il - tel: +972.52.368.4656, http://www.tkos.co.il -

WARNING: multiple messages have this Message-ID (diff)
From: Baruch Siach <baruch@tkos.co.il>
To: "Christoph Lameter (Ampere)" <cl@linux.com>
Cc: "Christoph Hellwig" <hch@lst.de>,
	"Marek Szyprowski" <m.szyprowski@samsung.com>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Frank Rowand" <frowand.list@gmail.com>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Will Deacon" <will@kernel.org>,
	"Robin Murphy" <robin.murphy@arm.com>,
	iommu@lists.linux.dev, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, "Petr Tesařík" <petr@tesarici.cz>,
	"Ramon Fried" <ramon@neureality.ai>
Subject: Re: [PATCH RFC 1/4] of: get dma area lower limit
Date: Thu, 18 Jan 2024 12:59:58 +0200	[thread overview]
Message-ID: <87cytyx5gf.fsf@tarshish> (raw)
In-Reply-To: <30d81f73-e27e-6cc4-5458-686e3ddd2e5c@linux.com>

Hi Christoph

On Wed, Jan 17 2024, Christoph Lameter (Ampere) wrote:
> On Wed, 27 Dec 2023, Baruch Siach wrote:
>> of_dma_get_max_cpu_address() returns the highest CPU address that
>> devices can use for DMA. The implicit assumption is that all CPU
>> addresses below that limit are suitable for DMA. However the
>> 'dma-ranges' property this code uses also encodes a lower limit for DMA
>> that is potentially non zero.
>
> All of memory can be used for DMA by default (==ZONE_NORMAL). ZONE_DMA defines
> a special range for devices that are unable to perform DMA to all of
> memory. Usually due to the lack of address bit support.
>
> So I guess that the platform in question here has as a general limit as to
> what address spaces I/O devices can do DMA to?

DMA to/from devices in bus with 'dma-ranges' property is limited to
address space described in 'dma-ranges'. The arm64 platform currently
uses 'dma-ranges' as a hint to set ZONE_DMA limits globally. This series
is meant to make ZONE_DMA limits adjustment code work better for
platforms where the lower DMA limit is above 4GB. This commit adds the
ability to extract the lower limit from 'dma-ranges'.

baruch

-- 
                                                     ~. .~   Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
   - baruch@tkos.co.il - tel: +972.52.368.4656, http://www.tkos.co.il -

_______________________________________________
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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2024-01-18 11:10 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-12-27 15:04 [PATCH RFC 0/4] arm64: support DMA zone starting above 4GB Baruch Siach
2023-12-27 15:04 ` Baruch Siach
2023-12-27 15:04 ` [PATCH RFC 1/4] of: get dma area lower limit Baruch Siach
2023-12-27 15:04   ` Baruch Siach
2024-01-17 22:23   ` Christoph Lameter (Ampere)
2024-01-17 22:23     ` Christoph Lameter (Ampere)
2024-01-18 10:59     ` Baruch Siach [this message]
2024-01-18 10:59       ` Baruch Siach
2023-12-27 15:04 ` [PATCH RFC 2/4] of: unittest: add test for of_dma_get_cpu_limits() 'min' param Baruch Siach
2023-12-27 15:04   ` Baruch Siach
2023-12-27 15:04 ` [PATCH RFC 3/4] dma-direct: add offset to zone_dma_bits Baruch Siach
2023-12-27 15:04   ` Baruch Siach
2024-01-08 17:55   ` Catalin Marinas
2024-01-08 17:55     ` Catalin Marinas
2024-01-09 10:03     ` Baruch Siach
2024-01-09 10:03       ` Baruch Siach
2024-01-09 10:54       ` Catalin Marinas
2024-01-09 10:54         ` Catalin Marinas
2024-01-09 13:54         ` Baruch Siach
2024-01-09 13:54           ` Baruch Siach
2024-01-09 17:51           ` Catalin Marinas
2024-01-09 17:51             ` Catalin Marinas
2023-12-27 15:04 ` [PATCH RFC 4/4] arm64: mm: take DMA zone offset into account Baruch Siach
2023-12-27 15:04   ` Baruch Siach

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