On Tue, Nov 08, 2016 at 08:27:12AM +0100, Marek Szyprowski wrote: > On 2016-11-07 22:47, Luis R. Rodriguez wrote: > > If so > > why? If this issue is present also on systems that only use ACPI is > > this possibly due to an ACPI firmware bug or the lack of some semantics > > in ACPI to express ordering in a better way? If the issue is device > > tree related only is this due to the lack of semantics in device tree > > to express some more complex dependency ? > > The main feature of device links that is used in this patch is enabling > runtime pm dependency between Exynos SYSMMU controller (called it client > device) and the device, for which it implements DMA address translation > (called master device). The assumptions are following: > 1. master device driver is completely unaware of the Exynos SYSMMU presence, > IOMMU is transparently hooked up and managed by DMA-mapping framework > 2. SYSMMU belongs to the same power domain as it's master device > 3. SYSMMU is optional, master device can fully operate without it, with > simple DMA address translation (DMA address == physical address) > 4. Master device implements runtime pm, what in turn causes respective > power domain to be turned on/off > 5. DMA-mapping and IOMMU frameworks provides no calls to notify SYSMMU > when its master device is performing DMA operations, so SYSMMU has > to be runtime active > 6. Currently SYSMMU always sets its runtime pm status to active after > attaching to its master device to ensure proper hardware state. This > prevents power domain to be turned off, even when master device sets > its runtime pm status to suspended. > 7. Exynos SYSMMU has to be runtime active at the same time when its > master device is runtime active to it to perform DMA operations and > allow the power domain to be turned off, when master device is > runtime suspended. > 8. The terms of device links, Exynos SYSMMU is a 'consumer' and master > device is a 'supplier'. You seem to have mixed up the consumer and supplier in point 8 above. Your code is such that the SYSMMU is the supplier and the master device is the consumer: device_link_add(dev, data->sysmmu, DL_FLAG_PM_RUNTIME); Prototype of device_link_add: struct device_link *device_link_add(struct device *consumer, struct device *supplier, u32 flags); Your code is correct, only point 8 above is wrong. Best regards, Lukas -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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