On Wed, Dec 30, 2020 at 01:47:25PM +0100, Marek Vasut wrote: > On 12/21/20 11:01 AM, Lorenzo Pieralisi wrote: > > [...] > > > > > > > > --- a/drivers/pci/controller/pcie-rcar-host.c > > > > > > > +++ b/drivers/pci/controller/pcie-rcar-host.c > > > > > > > @@ -753,7 +753,7 @@ static int rcar_pcie_enable_msi(struct rcar_pcie_host *host) > > > > > > > } > > > > > > > /* setup MSI data target */ > > > > > > > - msi->pages = __get_free_pages(GFP_KERNEL, 0); > > > > > > > + msi->pages = __get_free_pages(GFP_KERNEL | GFP_DMA32, 0); > > > > > > > > > > > > This does not do what you want on !CONFIG_ZONE_DMA32 (ie arm LPAE). > > > > > > > > > > How come? I would expect GFP_DMA32 allocates a buffer below 4 GiB in any > > > > > case. > > > > > > > > For ARM LPAE allocation falls back to ZONE_NORMAL that happens to work > > > > because if there is memory > 4GB it ends up in ZONE_HIGHMEM, so this > > > > patch should still work on ARM LPAE too. > > > > > > > > Regardless, thoughts above the alternative approach (that saves you > > > > a page allocation) ? > > > > > > Since this is a bugfix, I would prefer it to be minimal. > > > > Yes, I agree with you on that. > > Then maybe it makes sense to apply this bugfix so others can benefit from it > too ? I will apply it shortly, thanks. > > > Also, in case there was some yet undiscovered hardware bug which would > > > let the MSI write through, having unused memory as the MSI destination > > > address would only lead to write into that memory -- instead of a > > > write into some other address. > > > > > > Changing this to some hard-coded address (any suggestions?) can be a > > > subsequent patch. > > > > The idea was taking the address from the host controller inbound window > > (ie an address outside the dma-ranges ~(dma-ranges) and < 4GB), it > > should not matter which one. > > Wouldn't that make the code quite unnecessarily complex for no gain ? Well, there is a gain, current code is allocating a page of memory - there is no need to do that and I don't think that what I am asking is complex. Again, I will merge this patch but please have a look to check if what I ask above is a possibility. Thanks, Lorenzo > The above fix does just that in one line, unless there is some code in the > PCI subsystem to select such an address already ? > > > I agree though that this can be a > > subsequent patch even though usually we send for -rc* only fixes for > > patches that hit the previous merge window - this seems a quite > > longstanding (I traced it back to v3.16) one so it would wait till > > v5.12, there is time to refactor it. > > I see, I was not aware of this policy toward bugfixes.
