Re: [PATCH] firmware: qcom_scm: fix error for incompatible pointer

From: Minwoo Im
Date: Tue Jul 23 2019 - 09:28:32 EST

> > > > We just can cast phys_addr_t to dma_addr_t here.
> > >
> > > IME, casting is rarely a proper solution.
> >
> > *nod*
> >
> > ptr_phys probably should be a dma_addr_t. Unless this driver is so
> > magic that it really wants a physical and not a dma address, in which
> > case it needs to use alloc_pages instead of dma_alloc_coherent
> > and then call page_to_phys on the returned page, and a very big comment
> > explaining why it is so special.
> The scm call takes physical addresses (which happens to be 1:1 with DMA
> addresses for this driver).
> This allocation started off (downstream) as a simple kmalloc(), but
> while the scm call is being executed an access from Linux will cause a
> security violation (that's not handled gracefully). The properties of
> dma_alloc is closer, so that's where the code is today.
> Optimally this should be something like alloc_pages() and some mechanism
> for unmapping the pages during the call. But no one has come up with a
> suitable patch for that.
> But there's a patch from Stephen for this already (not doing a
> typecast). Apparently I missed merging this, so I'll do that.


I appreciate for checking this. And also thanks all you guys for the
comments here!