On Wed, Nov 20, 2013 at 12:28:02PM +1100, Benjamin Herrenschmidt wrote: > On Tue, 2013-11-19 at 16:11 +0800, Li Zhong wrote: > > I encountered following issue: > > [ 0.283035] ibmvscsi 30000015: couldn't initialize event pool > > [ 5.688822] ibmvscsi: probe of 30000015 failed with error -1 > > > > which prevents the storage from being recognized, and the machine from > > booting. > > > > After some digging, it seems that it is caused by commit 4886c399da > > > > as dma_mask pointer in viodev->dev is not set, so in > > dma_set_mask_and_coherent(), dma_set_coherent_mask() is not called > > because dma_set_mask(), which is dma_set_mask_pSeriesLP() returned EIO. > > While before the commit, dma_set_coherent_mask() is always called. > > > > I tried to replace dma_set_mask_and_coherent() with > > dma_coerce_mask_and_coherent(), and the machine could boot again. > > > > But I'm not sure whether this is the correct fix... > > Russell, care to chime in ? I can't make sense of the semantics... > > The original commit was fairly clear: > > << > Replace the following sequence: > > dma_set_mask(dev, mask); > dma_set_coherent_mask(dev, mask); > > with a call to the new helper dma_set_mask_and_coherent(). > >> > > It all makes sense so far ... but doesn't work for some odd reason, > and the "fix" uses a function whose name doesn't make much sense to > me ... what is the difference between "setting" and "coercing" > the mask ? And why doe replacing two "set" with a "set both" doesn't > work and require a coerce ? > > I'm asking because I'm worried about breakage elsewhere...
I'd expect that the reason it doesn't work is that the dma_set_mask() is failing, which means we don't go on to set the coherent mask. Li Zong's patch works around the issue of a failing dma_set_mask(), but as I've already said elsewhere, the real fix is to get whatever created the struct device to initialise the dev->dma_mask with a bus default. Using dma_coerce_xxx() merely makes the problem "go away" papering over the issue - it's fine to do it this way, but someone should still fix the broken code creating these devices... _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
