[PATCH 1/2] arm64: dma_mapping: allow PCI host driver to limit DMA mask

Nikita Yushchenko
2017-01-03T20:23:06Z

>>>> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
>>>> index 290a84f..49645277 100644
>>>> --- a/arch/arm64/mm/dma-mapping.c
>>>> +++ b/arch/arm64/mm/dma-mapping.c
>>>> @@ -28,6 +28,7 @@
>>>> #include <linux/dma-contiguous.h>
>>>> #include <linux/vmalloc.h>
>>>> #include <linux/swiotlb.h>
>>>> +#include <linux/pci.h>
>>>>
>>>> #include <asm/cacheflush.h>
>>>>
>>>> @@ -347,6 +348,16 @@ static int __swiotlb_get_sgtable(struct device *dev, struct sg_table *sgt,
>>>>
>>>> static int __swiotlb_dma_supported(struct device *hwdev, u64 mask)
>>>> {
>>>> +#ifdef CONFIG_PCI
>>>> + if (dev_is_pci(hwdev)) {
>>>> + struct pci_dev *pdev = to_pci_dev(hwdev);
>>>> + struct pci_host_bridge *br = pci_find_host_bridge(pdev->bus);
>>>> +
>>>> + if (br->dev.dma_mask && (*br->dev.dma_mask) &&
>>>> + (mask & (*br->dev.dma_mask)) != mask)
>>>> + return 0;
>>>> + }
>>>> +#endif
>>>
>>> Hmm, but this makes it look like the problem is both arm64 and swiotlb
>>> specific, when in reality it's not. Perhaps another hack you could try
>>> would be to register a PCI bus notifier in the host bridge looking for
>>> BUS_NOTIFY_BIND_DRIVER, then you could proxy the DMA ops for each child
>>> device before the driver has probed, but adding a dma_set_mask callback
>>> to limit the mask to what you need?
>>
>> This is what Renesas BSP tries to do and it does not work.
>>
>> BUS_NOTIFY_BIND_DRIVER arrives after driver's probe routine exits, but
>> i/o can be started before that.
>
> Hm. This is strange statement:
> really_probe
> |->driver_sysfs_add
> |-> blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
> BUS_NOTIFY_BIND_DRIVER, dev);
> ...
> |- ret = drv->probe(dev);
> ...
> |- driver_bound(dev);
> |- blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
> BUS_NOTIFY_BOUND_DRIVER, dev);
>
> Am I missing smth?

I misinterpreted your message, sorry.

BSP attaches to BUS_NOTIFY_BOUND_DRIVER, not to BUS_NOTIFY_BIND_DRIVER,
and simply overwrites device's dma_mask there. You are suggesting
something completely different.

I'll check if your approach is practical.

Currently powerpc architecture has one more approach implemented, they
use pci_controller structure provided by host bridge driver, and that
has a set_dma_mask() hook. Maybe extending this beyond powerpc could be
a good idea. However, that will require changing quite a few host bridge
drivers, without any gain for most of those...