From: David Hildenbrand <david@redhat.com>
To: Miles Chen <miles.chen@mediatek.com>,
Joerg Roedel <joro@8bytes.org>,
Matthias Brugger <matthias.bgg@gmail.com>
Cc: wsd_upstream@mediatek.com, linux-kernel@vger.kernel.org,
Chao Hao <chao.hao@mediatek.com>,
iommu@lists.linux-foundation.org,
linux-mediatek@lists.infradead.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] iommu/mediatek: Use totalram_pages to setup enable_4GB
Date: Thu, 4 Jun 2020 10:25:15 +0200 [thread overview]
Message-ID: <55820901-430b-14c4-9426-7a4991ca0eed@redhat.com> (raw)
In-Reply-To: <20200604080120.2628-1-miles.chen@mediatek.com>
On 04.06.20 10:01, Miles Chen wrote:
> To build this driver as a kernel module, we cannot use
> the unexported symbol "max_pfn" to setup enable_4GB.
>
> Use totalram_pages() instead to setup enable_4GB.
>
> Suggested-by: Mike Rapoport <rppt@linux.ibm.com>
> Signed-off-by: Miles Chen <miles.chen@mediatek.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Yong Wu <yong.wu@mediatek.com>
> Cc: Chao Hao <chao.hao@mediatek.com>
> ---
> drivers/iommu/mtk_iommu.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index 5f4d6df59cf6..c2798a6e0e38 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -3,7 +3,6 @@
> * Copyright (c) 2015-2016 MediaTek Inc.
> * Author: Yong Wu <yong.wu@mediatek.com>
> */
> -#include <linux/memblock.h>
> #include <linux/bug.h>
> #include <linux/clk.h>
> #include <linux/component.h>
> @@ -626,8 +625,8 @@ static int mtk_iommu_probe(struct platform_device *pdev)
> return -ENOMEM;
> data->protect_base = ALIGN(virt_to_phys(protect), MTK_PROTECT_PA_ALIGN);
>
> - /* Whether the current dram is over 4GB */
> - data->enable_4GB = !!(max_pfn > (BIT_ULL(32) >> PAGE_SHIFT));
> + /* Whether the current dram is over 4GB, note: DRAM start at 1GB */
> + data->enable_4GB = !!(totalram_pages() > ((SZ_2G + SZ_1G) >> PAGE_SHIFT));
A similar thing seems to be done by
drivers/media/platform/mtk-vpu/mtk_vpu.c:
vpu->enable_4GB = !!(totalram_pages() > (SZ_2G >> PAGE_SHIFT));
I do wonder if some weird memory hotplug setups might give you false
negatives.
E.g., start a VM with 1GB and hotplug 1GB - it will be hotplugged on
x86-64 above 4GB, turning max_pfn into 5GB. totalram_pages() should
return something < 2GB.
Same can happen when you have a VM and use ballooning to fake-unplug
memory, making totalram_pages() return something < 4GB, but leaving
usable pfns >= 4GB.
but
... I don't know if I understood what "enable_4GB" needs/implies
... I don't know if this is applicable to VMs at all (on real HW such
memory hotplug setups should not exist)
... I don't know how this code would react to memory hotplug, so if the
condition changes after the driver loaded and enable_4GB would
suddenly apply. Again, most probably not relevant on real HW, only
for VMs.
--
Thanks,
David / dhildenb
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next prev parent reply other threads:[~2020-06-04 8:25 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-04 8:01 [PATCH] iommu/mediatek: Use totalram_pages to setup enable_4GB Miles Chen
2020-06-04 8:25 ` David Hildenbrand [this message]
2020-06-04 9:49 ` Miles Chen
2020-06-04 11:32 ` David Hildenbrand
2020-06-04 15:06 ` Christoph Hellwig
2020-06-04 15:27 ` David Hildenbrand
2020-06-05 12:52 ` David Hildenbrand
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