Re: [PATCH v3 8/9] PCI: rockchip-ep: Set a 64-bit BAR if requested

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Apr 12, 2024 at 11:39:39PM +0200, Niklas Cassel wrote:
> On Fri, Apr 12, 2024 at 12:51:27PM -0500, Bjorn Helgaas wrote:
> > On Wed, Mar 13, 2024 at 11:58:00AM +0100, Niklas Cassel wrote:
> > > Ever since commit f25b5fae29d4 ("PCI: endpoint: Setting a BAR size > 4 GB
> > > is invalid if 64-bit flag is not set") it has been impossible to get the
> > > .set_bar() callback with a BAR size > 4 GB, if the BAR was also not
> > > requested to be configured as a 64-bit BAR.
> > > 
> > > It is however possible that an EPF driver configures a BAR as 64-bit,
> > > even if the requested size is < 4 GB.
> > > 
> > > Respect the requested BAR configuration, just like how it is already
> > > repected with regards to the prefetchable bit.
> > 
> > Does this (and the similar cadence patch) need a Fixes: tag for
> > f25b5fae29d4?
> 
> I don't think so.
> 
> Both patches are about respecting the configuration requested by an EPF
> driver.
> 
> So if an EPF driver requests a 64-bit BAR, the EPC driver should configure
> that. (Regardless of the size that the EPF driver requests for the BAR.)
> 
> If we really want a Fixes-tag, I would imagine that it will be the respective
> initial commits that added these drivers (pcie-cadence-ep.c and
> pcie-rockchip-ep.c), as it has been this way since then.
> 
> If you look at the EPF drivers we currently have, they will currently only
> request a 64-bit BAR if any of the BARs can only be configured as a 64-bit
> BAR because of hardware limitiations.
> 
> $ git grep only_64bit
> 
> Neither of these two drivers have any such hardware limitiations,
> so these commits are currently a bit pointless.
> 
> However, the drivers should of course do the right thing, because other
> EPC drivers might look at them and copy their code.
> 
> And who knows, maybe sometime in the future there will be an EPF driver
> that will explicitly request a 64-bit BAR, regardless of size.
> 
> TL;DR: I don't think these two commits are worth backporting.

OK, thanks!

> > > Signed-off-by: Niklas Cassel <cassel@kernel.org>
> > > ---
> > >  drivers/pci/controller/pcie-rockchip-ep.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/pci/controller/pcie-rockchip-ep.c b/drivers/pci/controller/pcie-rockchip-ep.c
> > > index c9046e97a1d2..57472cf48997 100644
> > > --- a/drivers/pci/controller/pcie-rockchip-ep.c
> > > +++ b/drivers/pci/controller/pcie-rockchip-ep.c
> > > @@ -153,7 +153,7 @@ static int rockchip_pcie_ep_set_bar(struct pci_epc *epc, u8 fn, u8 vfn,
> > >  		ctrl = ROCKCHIP_PCIE_CORE_BAR_CFG_CTRL_IO_32BITS;
> > >  	} else {
> > >  		bool is_prefetch = !!(flags & PCI_BASE_ADDRESS_MEM_PREFETCH);
> > > -		bool is_64bits = sz > SZ_2G;
> > > +		bool is_64bits = !!(flags & PCI_BASE_ADDRESS_MEM_TYPE_64);
> > >  
> > >  		if (is_64bits && (bar & 1))
> > >  			return -EINVAL;
> > > -- 
> > > 2.44.0
> > > 
> 
> _______________________________________________
> Linux-rockchip mailing list
> Linux-rockchip@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-rockchip

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