On Thu, Feb 25, 2016 at 11:52 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: >> Actually even if we specify a dma-ranges on the parent DT node, the >> DMA range will still be limited to 32 bits because of the following >> code in of_dma_configure(): >> >> /* >> * Set default coherent_dma_mask to 32 bit. Drivers are expected to >> * setup the correct supported mask. >> */ >> if (!dev->coherent_dma_mask) >> dev->coherent_dma_mask = DMA_BIT_MASK(32); >> >> /* >> * Set it to coherent_dma_mask by default if the architecture >> * code has not set it. >> */ >> if (!dev->dma_mask) >> dev->dma_mask = &dev->coherent_dma_mask; >> >> .... >> /* gets dma-ranges into dma_addr and size */ >> .... >> >> >> *dev->dma_mask = min((*dev->dma_mask), >> DMA_BIT_MASK(ilog2(dma_addr + size))); >> >> So unless the DMA mask is set on the device before of_dma_configure() >> is called, the min() statement will choose the 32 bits mask that has >> been previously set. So IIUC in any case, the driver will need to call >> dma_set_mask() > > Yes, the driver definitely has to call dma_set_mask(), the property of > the parent bus is used to make that fail when the bus doesn't support > it. And that's where things seem to stop working: the driver's probe function is invoked by the platform bus, *after* of_dma_configure() is called. So unless I am missing something there is no way for the driver to set the DMA mask in such a way that of_dma_configure() can see it and do the right thing. In other words, most of the DMA mask logic in of_dma_configure() doesn't seem to have any effect (and a 32 bits mask will be set), at least on the platform bus. >> Can I have your thoughts on this? Am I missing something? > > One point: I think the dma_set_mask() probably should be in the > generic part of the sdhci driver, not the tegra specific portion. Ok, but then how does the generic part of the driver knows which DMA mask applies to the device? > I also forget how this really needs to interact with swiotlb. I know > we have discussed this a couple of times, but the result currently > is lost to me. > Maybe the answer was that if swiotlb or iommu are enabled, then > dma_set_mask() should always succeed, but the mask should not actually > be updated? -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
