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 17:38:33 +0100
From:   Christian Zigotzky <chzigotzky@...osoft.de>
To:     Mike Rapoport <rppt@...ux.ibm.com>, 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
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 10:32 am, Mike Rapoport wrote:
> On Mon, Nov 25, 2019 at 08:39:23AM +0100, 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.
> Presuming the problem is relevant for all CoreNet boards something like
> this could work:
>   
> diff --git a/arch/powerpc/include/asm/dma.h b/arch/powerpc/include/asm/dma.h
> index 1b4f0254868f..7c6cfeeaff52 100644
> --- a/arch/powerpc/include/asm/dma.h
> +++ b/arch/powerpc/include/asm/dma.h
> @@ -347,5 +347,11 @@ extern int isa_dma_bridge_buggy;
>   #define isa_dma_bridge_buggy	(0)
>   #endif
>   
> +#ifdef CONFIG_CORENET_GENERIC
> +extern phys_addr_t ppc_dma_phys_limit;
> +#define ARCH_LOW_ADDRESS_LIMIT	(ppc_dma_phys_limit - 1)
> +#endif
> +
> +
>   #endif /* __KERNEL__ */
>   #endif	/* _ASM_POWERPC_DMA_H */
> diff --git a/arch/powerpc/platforms/85xx/common.c b/arch/powerpc/platforms/85xx/common.c
> index fe0606439b5a..346b436b6d3f 100644
> --- a/arch/powerpc/platforms/85xx/common.c
> +++ b/arch/powerpc/platforms/85xx/common.c
> @@ -126,3 +126,7 @@ void __init mpc85xx_qe_par_io_init(void)
>   	}
>   }
>   #endif
> +
> +#ifdef CONFIG_CORENET_GENERIC
> +phys_addr_t ppc_dma_phys_limit = 0xffffffffUL;
> +#endif
> diff --git a/arch/powerpc/platforms/85xx/corenet_generic.c b/arch/powerpc/platforms/85xx/corenet_generic.c
> index 7ee2c6628f64..673bcbdc7c75 100644
> --- a/arch/powerpc/platforms/85xx/corenet_generic.c
> +++ b/arch/powerpc/platforms/85xx/corenet_generic.c
> @@ -64,7 +64,7 @@ void __init corenet_gen_setup_arch(void)
>   	mpc85xx_smp_init();
>   
>   	swiotlb_detect_4g();
> -
> +	ppc_dma_phys_limit = 0x0fffffffUL;
>   	pr_info("%s board\n", ppc_md.name);
>   
>   	mpc85xx_qe_init();
>
>> 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 Mike,

Many thanks for your patch! I will test it tomorrow.

Cheers,
Christian