Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/2] of: device: Allow DMA range map to be set before of_dma_configure_id | From | Robin Murphy <> | Date | Mon, 18 Jan 2021 13:27:44 +0000 |
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On 2021-01-16 17:07, Paul Kocialkowski wrote: > Hi Robin, > > Le Sat 16 Jan 21, 14:57, Robin Murphy a écrit : >> On 2021-01-15 17:58, Paul Kocialkowski wrote: >>> A mechanism was recently introduced for the sunxi architecture where >>> the DMA offset for specific devices (under the MBUS) is set by a common >>> driver (sunxi_mbus). This driver calls dma_direct_set_offset to set >>> the device's dma_range_map manually. >>> >>> However this information was overwritten by of_dma_configure_id, which >>> obtains the map from of_dma_get_range (or keeps it NULL when it fails >>> and the force_dma argument is true, which is the case for platform >>> devices). >>> >>> As a result, the dma_range_map was always overwritten and the mechanism >>> could not correctly take effect. >>> >>> This adds a check to ensure that no previous DMA range map is >>> overwritten and prints a warning when the map was already set while >>> also being available from dt. In this case, the map that was already >>> set is kept. >> >> Hang on, the hard-coded offset is only intended to be installed when there >> *isn't* anything described in DT, in which case of_dma_get_range() should >> always bail out early without touching it anyway. This sounds like >> something's not quite right in the MBUS driver, so I don't think working >> around it in core code is really the right thing to do. > > That's right, there is no practical case where the two are in conflict. > The problem that I'm solving here is that dev->dma_range_map is *always* > assigned, even when of_dma_get_range bailed and map still is NULL. > > This has the effect of always overwriting what the MBUS driver does > (and leaking its memory too).
Oh, I should have looked closer at of_dma_configure_id() itself. I was assuming that b4bdc4fbf8d0 had been tested and at least *could* work, but apparently not :/
Indeed it seems there was a fundamental oversight in e0d072782c73 ("dma-mapping: introduce DMA range map, supplanting dma_pfn_offset"), equivalent to the same one I previously made myself with bus_dma_mask and fixed in 6778be4e5209 ("of/device: Really only set bus DMA mask when appropriate"). I think same simpler fix is the right one for this case too, i.e. just move the assignment to dev->dma_range_map up under the "if (!ret)" condition. Assigning it this late - after the IOMMU and arch setup - looks wrong anyway, even if it isn't currently an issue in practice (in principle an IOMMU driver *could* start trying to figure out reserved regions around DMA windows for a device as early as its .of_xlate callback, even though that's not the intent of the API design).
Luckily dma_range_map hasn't been hooked up in the equivalent ACPI path yet, so you're off the hook for fixing that too :)
Cheers, Robin.
>> Do you have a case where one of the relevant devices inherits a "dma-ranges" >> via the regular hierarchy without indirecting via an "interconnects" >> reference? Currently you're only checking for the latter, so that would be >> one way things could go awry (although to be a problem, said "dma-ranges" >> would also have to encode something *other* than the appropriate MBUS >> offset, which implies an incorrect or at least inaccurately-structured DT as >> well). > > No, I think things are good in that regard. No messed up dt or anything like > that :) > > Cheers, > > Paul > >> Robin. >> >>> Fixes: b4bdc4fbf8d0 ("soc: sunxi: Deal with the MBUS DMA offsets in a central place") >>> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com> >>> --- >>> drivers/of/device.c | 9 ++++++++- >>> 1 file changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/of/device.c b/drivers/of/device.c >>> index aedfaaafd3e7..db1b8634c2c7 100644 >>> --- a/drivers/of/device.c >>> +++ b/drivers/of/device.c >>> @@ -181,7 +181,14 @@ int of_dma_configure_id(struct device *dev, struct device_node *np, >>> arch_setup_dma_ops(dev, dma_start, size, iommu, coherent); >>> - dev->dma_range_map = map; >>> + if (!dev->dma_range_map) { >>> + dev->dma_range_map = map; >>> + } else if (map) { >>> + dev_warn(dev, >>> + "DMA range map was already set, ignoring range map from dt\n"); >>> + kfree(map); >>> + } >>> + >>> return 0; >>> } >>> EXPORT_SYMBOL_GPL(of_dma_configure_id); >>> >
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