Re: [PATCH v2] powerpc/powernv/pci-ioda: fix kdump with non-power-of-2 crashkernel=

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> From: "Nishanth Aravamudan" <nacc@linux.vnet.ibm.com>
> To: "Michael Ellerman" <mpe@ellerman.id.au>
> Cc: "Hari Bathini" <hbathini@in.ibm.com>, "Gavin Shan" <gwshan@linux.vnet.ibm.com>, "Alexey Kardashevskiy"
> <aik@ozlabs.ru>, "Ben Herrenschmidt" <benh@kernel.crashing.org>, "Paul Mackerras" <paulus@samba.org>, "David Gibson"
> <david@gibson.dropbear.id.au>, "Wei Yang" <weiyang@linux.vnet.ibm.com>, linuxppc-dev@lists.ozlabs.org, "Jan Stancek"
> <jstancek@redhat.com>
> Sent: Friday, 4 September, 2015 8:22:52 PM
> Subject: [PATCH v2] powerpc/powernv/pci-ioda: fix kdump with non-power-of-2 crashkernel=
> 
> The 32-bit TCE table initialization relies on the DMA window having a
> size equal to a power of 2 (and checks for it explicitly). But
> crashkernel= has no constraint that requires a power-of-2 be specified.
> This causes the kdump kernel to fail to boot as none of the PCI devices
> (including the disk controller) are successfully initialized.
> 
> After this change, the PCI devices successfully set up the 32-bit TCE
> table and kdump succeeds.
> 
> Fixes: aca6913f5551 ("powerpc/powernv/ioda2: Introduce helpers to allocate
> TCE pages")
> Signed-off-by: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
> Cc: stable@vger.kernel.org # 4.2

Tested-by: Jan Stancek <jstancek@redhat.com>

I can confirm, that this patch along with 
  http://patchwork.ozlabs.org/patch/513229/
applied on top of 4.2 is fixing kdump for me on Power S812L.
(ppc64le bare metal, crashkernel=1024M)

Regards,
Jan

> 
> ---
> 
> Michael, I kept this as a follow-on patch to my previous one. If you'd
> rather I made a v3 of that patch with the two fixes combined, I can
> resend. Also, I fixed up the context on my end to be u64, but not sure
> if that will match your tree (next doesn't have my prior patch applied
> yet, that I can see).
> 
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c
> b/arch/powerpc/platforms/powernv/pci-ioda.c
> index f1c74c28e564..d5e635f2c3aa 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -2078,12 +2078,18 @@ static long pnv_pci_ioda2_setup_default_config(struct
> pnv_ioda_pe *pe)
>  	struct iommu_table *tbl = NULL;
>  	long rc;
>  	/*
> +	 * crashkernel= specifies the kdump kernel's maximum memory at
> +	 * some offset and there is no guaranteed the result is a power
> +	 * of 2, which will cause errors later.
> +	 */
> +	const u64 max_memory = __rounddown_pow_of_two(memory_hotplug_max());
> +	/*
>  	 * In memory constrained environments, e.g. kdump kernel, the
>  	 * DMA window can be larger than available memory, which will
>  	 * cause errors later.
>  	 */
>  	const u64 window_size =
> -		min((u64)pe->table_group.tce32_size, memory_hotplug_max());
> +		min((u64)pe->table_group.tce32_size, max_memory);
>  
>  	rc = pnv_pci_ioda2_create_table(&pe->table_group, 0,
>  			iommu_page_shift_4k,
> 
>