linux-kernel - Re: [PATCH v4 2/3] PCI: dwc: ep: Add per-PF BAR and inbound ATU mapping support

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Message-ID: <aXyMWIHy_gMnIxOX@ryzen>
Date: Fri, 30 Jan 2026 11:47:52 +0100
From: Niklas Cassel <cassel@...nel.org>
To: Aksh Garg <a-garg7@...com>
Cc: Koichiro Den <den@...inux.co.jp>, linux-pci@...r.kernel.org,
	jingoohan1@...il.com, mani@...nel.org, lpieralisi@...nel.org,
	kwilczynski@...nel.org, robh@...nel.org, bhelgaas@...gle.com,
	Zhiqiang.Hou@....com, gustavo.pimentel@...opsys.com,
	linux-kernel@...r.kernel.org, s-vadapalli@...com,
	danishanwar@...com
Subject: Re: [PATCH v4 2/3] PCI: dwc: ep: Add per-PF BAR and inbound ATU
 mapping support

On Fri, Jan 30, 2026 at 04:09:26PM +0530, Aksh Garg wrote:
> On 30/01/26 15:23, Niklas Cassel wrote:
> > On Fri, Jan 30, 2026 at 09:42:43AM +0530, Aksh Garg wrote:
> > > On 29/01/26 19:44, Niklas Cassel wrote:
> > > > On Thu, Jan 29, 2026 at 02:47:52PM +0530, Aksh Garg wrote:
> > > > > -static void dw_pcie_ep_clear_ib_maps(struct dw_pcie_ep *ep, enum pci_barno bar)
> > > > > +static void dw_pcie_ep_clear_ib_maps(struct dw_pcie_ep *ep, u8 func_no, enum pci_barno bar)
> > > > >  {
> > > > > +	struct dw_pcie_ep_func *ep_func = dw_pcie_ep_get_func_from_ep(ep, func_no);
> > > > >  	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
> > > > >  	struct device *dev = pci->dev;
> > > > >  	unsigned int i, num;
> > > > > @@ -152,18 +157,18 @@ static void dw_pcie_ep_clear_ib_maps(struct dw_pcie_ep *ep, enum pci_barno bar)
> > > > >  	u32 *indexes;
> > > > > Hello Aksh,
> > > > > Considering that all other functions that you have modified, you
> > > have added a:
> > > > > if (!ep_func)
> > > > 	return;
> > > > > > I think you should do the same to this function.
> > > >
> > > 
> > > I omitted this NULL check here because all the current call sites of
> > > dw_pcie_ep_clear_ib_maps() already perform this validation. I felt
> > > adding it here would add redundancy in the code.
> > 
> > Ok, but with that logic, shouldn't we also remove the NULL checks from
> > dw_pcie_ep_ib_atu_bar() and dw_pcie_ep_ib_atu_addr(), because they are
> > only called from dw_pcie_ep_set_bar(), which already has the ep_func
> > NULL check?
> > 
> 
> Yes, that's correct. Alternatively, we can add the NULL check in
> dw_pcie_ep_clear_ib_maps() as well, making all the functions using
> ep_func self-contained and defensive, removing the dependency on whether
> the callers perform NULL checks. This makes the code more future proof,
> as new callers won't need to be aware of the NULL pointer possibility.

Sounds like a good idea to me.

Neither of these functions is in the hot path, so the performance of having
one less NULL check is not super critical.


Kind regards,
Niklas