linux-kernel - Re: Bug 205201 - Booting halts if Dawicontrol DC-2976 UW SCSI board installed, unless RAM size limited to 3500M

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Date:   Mon, 25 Nov 2019 17:36:17 +0100
From:   Christian Zigotzky <chzigotzky@...osoft.de>
To:     Christoph Hellwig <hch@....de>
Cc:     Robin Murphy <robin.murphy@....com>, linux-arch@...r.kernel.org,
        darren@...vens-zone.net, mad skateman <madskateman@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        iommu@...ts.linux-foundation.org, Rob Herring <robh+dt@...nel.org>,
        paulus@...ba.org, rtd2@...a.co.nz,
        "contact@...on.com" <contact@...on.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        nsaenzjulienne@...e.de, Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: Bug 205201 - Booting halts if Dawicontrol DC-2976 UW SCSI board
 installed, unless RAM size limited to 3500M

On 25 November 2019 at 08:39 am, Christoph Hellwig wrote:
> On Sat, Nov 23, 2019 at 12:42:27PM +0100, Christian Zigotzky wrote:
>> Hello Christoph,
>>
>> Please find attached the dmesg of your Git kernel.
> Thanks.  It looks like on your platform the swiotlb buffer isn't
> actually addressable based on the bus dma mask limit, which is rather
> interesting.  swiotlb_init uses memblock_alloc_low to allocate the
> buffer, and I'll need some help from Mike and the powerpc maintainers
> to figure out how that select where to allocate the buffer from, and
> how we can move it to a lower address.  My gut feeling would be to try
> to do what arm64 does and define a new ARCH_LOW_ADDRESS_LIMIT, preferably
> without needing too much arch specific magic.
>
> As a quick hack can you try this patch on top of the tree from Friday?
>
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index f491690d54c6..e3f95c362922 100644
> --- a/include/linux/memblock.h
> +++ b/include/linux/memblock.h
> @@ -344,7 +344,7 @@ static inline int memblock_get_region_node(const struct memblock_region *r)
>   #define MEMBLOCK_LOW_LIMIT 0
>   
>   #ifndef ARCH_LOW_ADDRESS_LIMIT
> -#define ARCH_LOW_ADDRESS_LIMIT  0xffffffffUL
> +#define ARCH_LOW_ADDRESS_LIMIT  0x0fffffffUL
>   #endif
>   
>   phys_addr_t memblock_phys_alloc_range(phys_addr_t size, phys_addr_t align,
>
Hello Christoph,

Thanks a lot for your help! I will test your patch tomorrow.

Cheers,
Christian