From: Robin Murphy <robin.murphy@arm.com>
To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
Catalin Marinas <catalin.marinas@arm.com>
Cc: phill@raspberryi.org, devicetree@vger.kernel.org,
f.fainelli@gmail.com, linux-mm@kvack.org, marc.zyngier@arm.com,
Will Deacon <will@kernel.org>,
linux-kernel@vger.kernel.org, eric@anholt.net,
iommu@lists.linux-foundation.org, robh+dt@kernel.org,
linux-rpi-kernel@lists.infradead.org, mbrugger@suse.com,
akpm@linux-foundation.org, frowand.list@gmail.com, hch@lst.de,
linux-arm-kernel@lists.infradead.org, wahrenst@gmx.net
Subject: Re: [PATCH 5/8] arm64: use ZONE_DMA on DMA addressing limited devices
Date: Thu, 1 Aug 2019 17:07:54 +0100 [thread overview]
Message-ID: <e35dd4a5-281b-d281-59c9-3fc7108eb8be@arm.com> (raw)
In-Reply-To: <d8b4a7cb9c06824ca88a0602a5bf38b6324b43c0.camel@suse.de>
On 2019-08-01 4:44 pm, Nicolas Saenz Julienne wrote:
> On Wed, 2019-07-31 at 18:07 +0100, Catalin Marinas wrote:
>> On Wed, Jul 31, 2019 at 05:47:48PM +0200, Nicolas Saenz Julienne wrote:
>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>> index 1c4ffabbe1cb..f5279ef85756 100644
>>> --- a/arch/arm64/mm/init.c
>>> +++ b/arch/arm64/mm/init.c
>>> @@ -50,6 +50,13 @@
>>> s64 memstart_addr __ro_after_init = -1;
>>> EXPORT_SYMBOL(memstart_addr);
>>>
>>> +/*
>>> + * We might create both a ZONE_DMA and ZONE_DMA32. ZONE_DMA is needed if
>>> there
>>> + * are periferals unable to address the first naturally aligned 4GB of ram.
>>> + * ZONE_DMA32 will be expanded to cover the rest of that memory. If such
>>> + * limitations doesn't exist only ZONE_DMA32 is created.
>>> + */
>>
>> Shouldn't we instead only create ZONE_DMA to cover the whole 32-bit
>> range and leave ZONE_DMA32 empty? Can__GFP_DMA allocations fall back
>> onto ZONE_DMA32?
>
> Hi Catalin, thanks for the review.
>
> You're right, the GFP_DMA page allocation will fail with a nasty dmesg error if
> ZONE_DMA is configured but empty. Unsurprisingly the opposite situation is fine
> (GFP_DMA32 with an empty ZONE_DMA32).
Was that tested on something other than RPi4 with more than 4GB of RAM?
(i.e. with a non-empty ZONE_NORMAL either way)
Robin.
> I switched to the scheme you're suggesting for the next version of the series.
> The comment will be something the likes of this:
>
> /*
> * We create both a ZONE_DMA and ZONE_DMA32. ZONE_DMA's size is decided based
> * on whether the SoC's peripherals are able to address the first naturally
> * aligned 4 GB of ram.
> *
> * If limited, ZONE_DMA covers that area and ZONE_DMA32 the rest of that 32 bit
> * addressable memory.
> *
> * If not ZONE_DMA is expanded to cover the whole 32 bit addressable memory and
> * ZONE_DMA32 is left empty.
> */
>
> Regards,
> Nicolas
>
>
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next prev parent reply other threads:[~2019-08-01 16:08 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-31 15:47 [PATCH 0/8] Raspberry Pi 4 DMA addressing support Nicolas Saenz Julienne
2019-07-31 15:47 ` [PATCH 1/8] arm64: mm: use arm64_dma_phys_limit instead of calling max_zone_dma_phys() Nicolas Saenz Julienne
2019-07-31 15:47 ` [PATCH 2/8] arm64: rename variables used to calculate ZONE_DMA32's size Nicolas Saenz Julienne
2019-07-31 15:47 ` [PATCH 3/8] of/fdt: add function to get the SoC wide DMA addressable memory size Nicolas Saenz Julienne
2019-08-02 17:17 ` Rob Herring
2019-08-05 16:03 ` Nicolas Saenz Julienne
2019-08-05 19:23 ` Rob Herring
2019-08-06 18:12 ` Nicolas Saenz Julienne
2019-08-08 15:02 ` Rob Herring
2019-08-08 17:30 ` Nicolas Saenz Julienne
2019-07-31 15:47 ` [PATCH 4/8] arm64: re-introduce max_zone_dma_phys() Nicolas Saenz Julienne
2019-07-31 15:47 ` [PATCH 5/8] arm64: use ZONE_DMA on DMA addressing limited devices Nicolas Saenz Julienne
2019-07-31 17:07 ` Catalin Marinas
2019-08-01 15:44 ` Nicolas Saenz Julienne
2019-08-01 16:07 ` Robin Murphy [this message]
2019-08-01 16:40 ` Nicolas Saenz Julienne
2019-07-31 15:47 ` [PATCH 6/8] dma-direct: turn ARCH_ZONE_DMA_BITS into a variable Nicolas Saenz Julienne
2019-08-01 14:04 ` Christoph Hellwig
2019-08-01 15:59 ` Nicolas Saenz Julienne
2019-07-31 15:47 ` [PATCH 7/8] arm64: update arch_zone_dma_bits to fine tune dma-direct min mask Nicolas Saenz Julienne
2019-07-31 15:47 ` [PATCH 8/8] mm: comment arm64's usage of 'enum zone_type' Nicolas Saenz Julienne
2019-08-01 14:08 ` Christoph Hellwig
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