Re: [PATCH 2/3] iommu/pci: reserve iova for PCI masters

[Oza Oza <oza.oza@broadcom.com>]

On Thu, May 4, 2017 at 11:50 PM, Robin Murphy <robin.murphy@arm.com> wrote:
> On 03/05/17 05:46, Oza Pawandeep wrote:
>> this patch reserves the iova for PCI masters.
>> ARM64 based SOCs may have scattered memory banks.
>> such as iproc based SOC has
>>
>> <0x00000000 0x80000000 0x0 0x80000000>, /* 2G @ 2G */
>> <0x00000008 0x80000000 0x3 0x80000000>, /* 14G @ 34G */
>> <0x00000090 0x00000000 0x4 0x00000000>, /* 16G @ 576G */
>> <0x000000a0 0x00000000 0x4 0x00000000>; /* 16G @ 640G */
>>
>> but incoming PCI transcation addressing capability is limited
>> by host bridge, for example if max incoming window capability
>> is 512 GB, then 0x00000090 and 0x000000a0 will fall beyond it.
>>
>> to address this problem, iommu has to avoid allocating iovas which
>> are reserved. which inturn does not allocate iova if it falls into hole.
>
> I don't necessarily disagree with doing this, as we could do with facing
> up to the issue of discontiguous DMA ranges in particular (I too have a
> platform with this problem), but I'm still not overly keen on pulling DT
> specifics into this layer. More than that, though, if we are going to do
> it, then we should do it for all devices with a restrictive
> "dma-ranges", not just PCI ones.
>

pci_create_root_bus allocates host bridge, and currently it takes only
oubound resources.

if inbound memory is also added as a part of  pci_create_root_bus params,
then IOVA allocation can directly make use of inbound_windows member
of structure pci_host_bridge.

struct pci_host_bridge {
        struct device dev;
        struct pci_bus *bus; /* root bus */
        struct list_head windows; /* resource_entry */
        struct list_head inbound_windows; /* resource_entry */
        .
        .
}

so iova_reserve_pci_windows can iterate throough
resource_list_for_each_entry(window, &bridge->inbound_windows)
this way we can remove the dependency of dma-iommu.c on OF layer.

but only thing is:
pci_create_root_bus is called by handful of RC drivers, which needs to change.
ideally if you see both inbound and outbound resource should belong to
pci_host_bridge anyway.
and inbound is completely missing.

let me know your thoughts on this, Robin.

>> Bug: SOC-5216
>> Change-Id: Icbfc99a045d730be143fef427098c937b9d46353
>> Signed-off-by: Oza Pawandeep <oza.oza@broadcom.com>
>> Reviewed-on: http://gerrit-ccxsw.broadcom.net/40760
>> Reviewed-by: vpx_checkpatch status <vpx_checkpatch@broadcom.com>
>> Reviewed-by: CCXSW <ccxswbuild@broadcom.com>
>> Tested-by: vpx_autobuild status <vpx_autobuild@broadcom.com>
>> Tested-by: vpx_smoketest status <vpx_smoketest@broadcom.com>
>> Tested-by: CCXSW <ccxswbuild@broadcom.com>
>> Reviewed-by: Scott Branden <scott.branden@broadcom.com>
>>
>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
>> index 48d36ce..08764b0 100644
>> --- a/drivers/iommu/dma-iommu.c
>> +++ b/drivers/iommu/dma-iommu.c
>> @@ -27,6 +27,7 @@
>>  #include <linux/iova.h>
>>  #include <linux/irq.h>
>>  #include <linux/mm.h>
>> +#include <linux/of_pci.h>
>>  #include <linux/pci.h>
>>  #include <linux/scatterlist.h>
>>  #include <linux/vmalloc.h>
>> @@ -171,8 +172,12 @@ static void iova_reserve_pci_windows(struct pci_dev *dev,
>>               struct iova_domain *iovad)
>>  {
>>       struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
>> +     struct device_node *np = bridge->dev.parent->of_node;
>>       struct resource_entry *window;
>>       unsigned long lo, hi;
>> +     int ret;
>> +     dma_addr_t tmp_dma_addr = 0, dma_addr;
>> +     LIST_HEAD(res);
>>
>>       resource_list_for_each_entry(window, &bridge->windows) {
>>               if (resource_type(window->res) != IORESOURCE_MEM &&
>> @@ -183,6 +188,36 @@ static void iova_reserve_pci_windows(struct pci_dev *dev,
>>               hi = iova_pfn(iovad, window->res->end - window->offset);
>>               reserve_iova(iovad, lo, hi);
>>       }
>> +
>> +     /* PCI inbound memory reservation. */
>> +     ret = of_pci_get_dma_ranges(np, &res);
>> +     if (!ret) {
>> +             resource_list_for_each_entry(window, &res) {
>> +                     struct resource *res_dma = window->res;
>> +
>> +                     dma_addr = res_dma->start - window->offset;
>> +                     if (tmp_dma_addr > dma_addr) {
>> +                             pr_warn("PCI: failed to reserve iovas; ranges should be sorted\n");
>
> I don't see anything in the DT spec about the entries having to be
> sorted, and it's not exactly impossible to sort a list if you need it so
> (and if I'm being really pedantic, one could still trigger this with a
> list that *is* sorted, only by different criteria).
>
> Robin.
>
>> +                             return;
>> +                     }
>> +                     if (tmp_dma_addr != dma_addr) {
>> +                             lo = iova_pfn(iovad, tmp_dma_addr);
>> +                             hi = iova_pfn(iovad, dma_addr - 1);
>> +                             reserve_iova(iovad, lo, hi);
>> +                     }
>> +                     tmp_dma_addr = window->res->end - window->offset;
>> +             }
>> +             /*
>> +              * the last dma-range should honour based on the
>> +              * 32/64-bit dma addresses.
>> +              */
>> +             if (tmp_dma_addr < DMA_BIT_MASK(sizeof(dma_addr_t) * 8)) {
>> +                     lo = iova_pfn(iovad, tmp_dma_addr);
>> +                     hi = iova_pfn(iovad,
>> +                                   DMA_BIT_MASK(sizeof(dma_addr_t) * 8) - 1);
>> +                     reserve_iova(iovad, lo, hi);
>> +             }
>> +     }
>>  }
>>
>>  /**
>>
>