linux-kernel - Re: [PATCH] PCI: dwc: rcar-gen4-ep: Program Resizable BARs and drop 1MiB BAR limit

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Message-ID: <3etnjc6pw2cpuvbdyl3q7rwkng2enxf63gtmpwk5oukeojwwtk@57o7h24egwfx>
Date: Wed, 11 Feb 2026 00:56:12 +0900
From: Koichiro Den <den@...inux.co.jp>
To: Niklas Cassel <cassel@...nel.org>
Cc: linux-pci@...r.kernel.org, linux-renesas-soc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, marek.vasut+renesas@...il.com, yoshihiro.shimoda.uh@...esas.com, 
	lpieralisi@...nel.org, kwilczynski@...nel.org, mani@...nel.org, robh@...nel.org, 
	bhelgaas@...gle.com, geert+renesas@...der.be, magnus.damm@...il.com
Subject: Re: [PATCH] PCI: dwc: rcar-gen4-ep: Program Resizable BARs and drop
 1MiB BAR limit

On Tue, Feb 10, 2026 at 04:33:32PM +0100, Niklas Cassel wrote:
> On Wed, Feb 11, 2026 at 12:31:21AM +0900, Koichiro Den wrote:
> > On Tue, Feb 10, 2026 at 11:25:16AM +0100, Niklas Cassel wrote:
> > > On Thu, Oct 23, 2025 at 04:22:17PM +0900, Koichiro Den wrote:
> > > > R-Car Gen4 (S4) exposes BAR0 and BAR2 as Resizable BARs. Program them
> > > > accordingly by using dw_pcie_ep_set_bar_resizable() instead of the
> > > > programmable BAR path.
> > > > 
> > > > Before this change the driver left the Resizable BAR capability
> > > > untouched and only wrote the BAR register, so the RC enumerated BAR0/2
> > > > as 1 MiB regardless of the size requested by the endpoint function. For
> > > > example, configuring a 2 MiB window for pci-epf-vntb still produced:
> > > > 
> > > >   ntb_hw_epf 0000:01:00.0: \
> > > >   Size:0x0000000000200000 is greater than the MW size 0x0000000000100000
> > > > 
> > > > Program the Resizable BAR control so the RC sees the requested size and
> > > > ntb_transport can use larger memory windows.
> > > > 
> > > > Signed-off-by: Koichiro Den <den@...inux.co.jp>
> > > > ---
> > > >  drivers/pci/controller/dwc/pcie-rcar-gen4.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > > 
> > > > diff --git a/drivers/pci/controller/dwc/pcie-rcar-gen4.c b/drivers/pci/controller/dwc/pcie-rcar-gen4.c
> > > > index 80778917d2dd..dbad741b8286 100644
> > > > --- a/drivers/pci/controller/dwc/pcie-rcar-gen4.c
> > > > +++ b/drivers/pci/controller/dwc/pcie-rcar-gen4.c
> > > > @@ -421,7 +421,9 @@ static int rcar_gen4_pcie_ep_raise_irq(struct dw_pcie_ep *ep, u8 func_no,
> > > >  
> > > >  static const struct pci_epc_features rcar_gen4_pcie_epc_features = {
> > > >  	.msi_capable = true,
> > > > +	.bar[BAR_0] = { .type = BAR_RESIZABLE, },
> > > >  	.bar[BAR_1] = { .type = BAR_RESERVED, },
> > > > +	.bar[BAR_2] = { .type = BAR_RESIZABLE, },
> > > >  	.bar[BAR_3] = { .type = BAR_RESERVED, },
> > > >  	.bar[BAR_4] = { .type = BAR_FIXED, .fixed_size = 256 },
> > > >  	.bar[BAR_5] = { .type = BAR_RESERVED, },
> > > > -- 
> > > > 2.48.1
> > > > 
> > > 
> > > Reviewed-by: Niklas Cassel <cassel@...nel.org>
> > > 
> > > Considering that this patch has not been picked up yet,
> > > perhaps resend it using [PATCH RESEND].
> > 
> > Thanks for the Reviewed-by. As almost four months have passed, in hindsight the
> > commit message sounds a bit too awkward now..
> > I'd like to update it to at least remove ntb-specific wording and make it more
> > compact and concise, like this:
> > 
> >   PCI: dwc: rcar-gen4-ep: Mark BAR0 and BAR2 as Resizable BARs
> > 
> >   R-Car Gen4 (S4) implements the PCIe Resizable BAR capability for BAR0 and
> >   BAR2. Advertise them as BAR_RESIZABLE so EPF-requested BAR sizes are
> >   reflected to the host.
> > 
> > If this looks good to you, would it be okay for me to keep the Reviewed-by
> > tag? There will be no code changes, only this commit message rewording in
> > the RESEND.
> 
> Looks good to me, and you can keep the R-b tag, but if you update the
> commit message, then you should probably send it as V2.

Will do, thanks for the confirmation.

Koichiro

> 
> 
> Kind regards,
> Niklas