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Message-ID: <20201027115010.GB32062@e121166-lin.cambridge.arm.com>
Date: Tue, 27 Oct 2020 11:50:10 +0000
From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc: robh+dt@...nel.org, catalin.marinas@....com, hch@....de,
ardb@...nel.org, linux-kernel@...r.kernel.org,
Hanjun Guo <guohanjun@...wei.com>,
Sudeep Holla <sudeep.holla@....com>, robin.murphy@....com,
linux-arm-kernel@...ts.infradead.org,
linux-rpi-kernel@...ts.infradead.org, jeremy.linton@....com,
iommu@...ts.linux-foundation.org, devicetree@...r.kernel.org,
will@...nel.org, Anshuman Khandual <anshuman.khandual@....com>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v4 6/7] arm64: mm: Set ZONE_DMA size based on early IORT
scan
On Wed, Oct 21, 2020 at 02:34:36PM +0200, Nicolas Saenz Julienne wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
>
> We recently introduced a 1 GB sized ZONE_DMA to cater for platforms
> incorporating masters that can address less than 32 bits of DMA, in
> particular the Raspberry Pi 4, which has 4 or 8 GB of DRAM, but has
> peripherals that can only address up to 1 GB (and its PCIe host
> bridge can only access the bottom 3 GB)
>
> Instructing the DMA layer about these limitations is straight-forward,
> even though we had to fix some issues regarding memory limits set in
> the IORT for named components, and regarding the handling of ACPI _DMA
> methods. However, the DMA layer also needs to be able to allocate
> memory that is guaranteed to meet those DMA constraints, for bounce
> buffering as well as allocating the backing for consistent mappings.
>
> This is why the 1 GB ZONE_DMA was introduced recently. Unfortunately,
> it turns out the having a 1 GB ZONE_DMA as well as a ZONE_DMA32 causes
> problems with kdump, and potentially in other places where allocations
> cannot cross zone boundaries. Therefore, we should avoid having two
> separate DMA zones when possible.
>
> So let's do an early scan of the IORT, and only create the ZONE_DMA
> if we encounter any devices that need it. This puts the burden on
> the firmware to describe such limitations in the IORT, which may be
> redundant (and less precise) if _DMA methods are also being provided.
> However, it should be noted that this situation is highly unusual for
> arm64 ACPI machines. Also, the DMA subsystem still gives precedence to
> the _DMA method if implemented, and so we will not lose the ability to
> perform streaming DMA outside the ZONE_DMA if the _DMA method permits
> it.
>
> Cc: Jeremy Linton <jeremy.linton@....com>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Cc: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Hanjun Guo <guohanjun@...wei.com>
> Cc: Sudeep Holla <sudeep.holla@....com>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> [nsaenz: Rebased, removed documentation change and add declaration in acpi_iort.h]
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
>
> ---
>
> Changes since v3:
> - Use min_not_zero()
> - Check ACPI revision
> - Remove unnecessary #ifdef in zone_sizes_init()
>
> arch/arm64/mm/init.c | 3 ++-
> drivers/acpi/arm64/iort.c | 52 +++++++++++++++++++++++++++++++++++++++
> include/linux/acpi_iort.h | 4 +++
> 3 files changed, 58 insertions(+), 1 deletion(-)
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 94e38f99748b..f5d4f85506e4 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -29,6 +29,7 @@
> #include <linux/kexec.h>
> #include <linux/crash_dump.h>
> #include <linux/hugetlb.h>
> +#include <linux/acpi_iort.h>
>
> #include <asm/boot.h>
> #include <asm/fixmap.h>
> @@ -190,7 +191,7 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
>
> #ifdef CONFIG_ZONE_DMA
> dt_zone_dma_bits = ilog2(of_dma_get_max_cpu_address(NULL));
> - zone_dma_bits = min(32U, dt_zone_dma_bits);
> + zone_dma_bits = min3(32U, dt_zone_dma_bits, acpi_iort_get_zone_dma_size());
> arm64_dma_phys_limit = max_zone_phys(zone_dma_bits);
> max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit);
> #endif
> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> index 9929ff50c0c0..05fe4a076bab 100644
> --- a/drivers/acpi/arm64/iort.c
> +++ b/drivers/acpi/arm64/iort.c
> @@ -1718,3 +1718,55 @@ void __init acpi_iort_init(void)
>
> iort_init_platform_devices();
> }
> +
> +#ifdef CONFIG_ZONE_DMA
> +/*
> + * Check the IORT whether any devices exist whose DMA mask is < 32 bits.
> + * If so, return the smallest value encountered, or 32 otherwise.
> + */
> +unsigned int __init acpi_iort_get_zone_dma_size(void)
> +{
> + struct acpi_table_iort *iort;
> + struct acpi_iort_node *node, *end;
> + acpi_status status;
> + u8 limit = 32;
> + int i;
> +
> + if (acpi_disabled)
> + return limit;
> +
> + status = acpi_get_table(ACPI_SIG_IORT, 0,
> + (struct acpi_table_header **)&iort);
> + if (ACPI_FAILURE(status))
> + return limit;
> +
> + node = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->node_offset);
> + end = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->header.length);
> +
> + for (i = 0; i < iort->node_count; i++) {
> + if (node >= end)
> + break;
> +
> + switch (node->type) {
> + struct acpi_iort_named_component *ncomp;
> + struct acpi_iort_root_complex *rc;
> +
> + case ACPI_IORT_NODE_NAMED_COMPONENT:
> + ncomp = (struct acpi_iort_named_component *)node->node_data;
> + limit = min_not_zero(limit, ncomp->memory_address_limit);
> + break;
> +
> + case ACPI_IORT_NODE_PCI_ROOT_COMPLEX:
> + if (node->revision < 1)
> + break;
> +
> + rc = (struct acpi_iort_root_complex *)node->node_data;
> + limit = min_not_zero(limit, rc->memory_address_limit);
> + break;
> + }
> + node = ACPI_ADD_PTR(struct acpi_iort_node, node, node->length);
> + }
> + acpi_put_table(&iort->header);
> + return limit;
> +}
> +#endif
> diff --git a/include/linux/acpi_iort.h b/include/linux/acpi_iort.h
> index 20a32120bb88..7d2e184f0d4d 100644
> --- a/include/linux/acpi_iort.h
> +++ b/include/linux/acpi_iort.h
> @@ -38,6 +38,7 @@ void iort_dma_setup(struct device *dev, u64 *dma_addr, u64 *size);
> const struct iommu_ops *iort_iommu_configure_id(struct device *dev,
> const u32 *id_in);
> int iort_iommu_msi_get_resv_regions(struct device *dev, struct list_head *head);
> +unsigned int acpi_iort_get_zone_dma_size(void);
> #else
> static inline void acpi_iort_init(void) { }
> static inline u32 iort_msi_map_id(struct device *dev, u32 id)
> @@ -55,6 +56,9 @@ static inline const struct iommu_ops *iort_iommu_configure_id(
> static inline
> int iort_iommu_msi_get_resv_regions(struct device *dev, struct list_head *head)
> { return 0; }
> +
> +static inline unsigned int acpi_iort_get_zone_dma_size(void)
> +{ return 32; }
> #endif
>
> #endif /* __ACPI_IORT_H__ */
> --
> 2.28.0
>
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