[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <06f16b1a55eede3dc3e0bf31ff14eca89ab6f009.camel@linux.ibm.com>
Date: Fri, 01 Aug 2025 13:30:27 +0200
From: Gerd Bayer <gbayer@...ux.ibm.com>
To: Manivannan Sadhasivam <mani@...nel.org>,
Hans Zhang
<hans.zhang@...tech.com>
Cc: Arnd Bergmann <arnd@...nel.org>, Bjorn Helgaas <helgaas@...nel.org>,
Hans Zhang <18255117159@....com>, bhelgaas@...gle.com,
Alexander Gordeev
<agordeev@...ux.ibm.com>,
Christian Borntraeger
<borntraeger@...ux.ibm.com>,
Ilpo Järvinen
<ilpo.jarvinen@...ux.intel.com>,
jingoohan1@...il.com,
Krzysztof
Wilczyński <kwilczynski@...nel.org>,
linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
linux-next
<linux-next@...r.kernel.org>, linux-pci@...r.kernel.org,
Lorenzo Pieralisi
<lpieralisi@...nel.org>,
Rob Herring <robh@...nel.org>,
Niklas Schnelle
<schnelle@...ux.ibm.com>, geert@...ux-m68k.org
Subject: Re: [PATCH] PCI: Fix endianness issues in pci_bus_read_config()
On Fri, 2025-08-01 at 16:24 +0530, Manivannan Sadhasivam wrote:
<--- snip --->
> > > > > > The pci_bus_read_config() interface itself may have been a
> > > > > > mistake, can't the callers just use the underlying helpers
> > > > > > directly?
> > > > > >
> > > > >
> > > > > They can! Since the callers of this API is mostly the macros, we can easily
> > > > > implement the logic to call relevant accessors based on the requested size.
> > > > >
> > > > > Hans, could you please respin the series based the feedback since the series is
> > > > > dropped for 6.17.
> > > > >
> > > >
> > > > Dear all,
> > > >
> > > > I am once again deeply sorry for the problems that occurred in this series.
> > > > I only test pulling the ARM platform.
> > > >
> > > > Thank you very much, Gerd, for reporting the problem.
no worries!
> > > > Thank you all for your discussions and suggestions for revision.
> > > >
> > > > Hi Mani,
> > > >
> > > > Geert provided a solution. My patch based on this is as follows. Please
> > > > check if there are any problems.
> > > > https://lore.kernel.org/linux-pci/CAMuHMdVwFeV46oCid_sMHjXfP+yyGTpBfs9t3uaa=wRxNcSOAQ@mail.gmail.com/
> > > >
> > > > Also, please ask Gerd to help test whether it works properly. Thank you very
> > > > much.
> > > >
I found Geert's proposal intriguing for a quick resolution of the
issue. Yet, I have not tried that proposal, though.
Instead I spent some more cycles on Lukas' and Mani's question about
the value of the pci_bus_read_config() helper. So I changed
PCI_FIND_NEXT_CAP and PCI_FIND_NEXT_EXT_CAP to use size-aware versions
of read_cfg accessor functions like this:
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index ac954584d991..9e2f75ede95f 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -109,17 +109,17 @@ int pci_bus_read_config(void *priv, unsigned int
devfn, int where, u32 size,
({
\
int __ttl = PCI_FIND_CAP_TTL;
\
u8 __id, __found_pos = 0;
\
- u32 __pos = (start);
\
- u32 __ent;
\
+ u8 __pos = (start);
\
+ u16 __ent;
\
\
- read_cfg(args, __pos, 1, &__pos);
\
+ read_cfg##_byte(args, __pos, &__pos);
\
\
while (__ttl--) {
\
if (__pos < PCI_STD_HEADER_SIZEOF)
\
break;
\
\
__pos = ALIGN_DOWN(__pos, 4);
\
- read_cfg(args, __pos, 2, &__ent);
\
+ read_cfg##_word(args, __pos, &__ent);
\
\
__id = FIELD_GET(PCI_CAP_ID_MASK, __ent);
\
if (__id == 0xff)
\
@@ -158,7 +158,7 @@ int pci_bus_read_config(void *priv, unsigned int
devfn, int where, u32 size,
\
__ttl = (PCI_CFG_SPACE_EXP_SIZE - PCI_CFG_SPACE_SIZE) / 8;
\
while (__ttl-- > 0 && __pos >= PCI_CFG_SPACE_SIZE) {
\
- __ret = read_cfg(args, __pos, 4, &__header);
\
+ __ret = read_cfg##_dword(args, __pos, &__header);
\
if (__ret != PCIBIOS_SUCCESSFUL)
\
break;
\
\
This fixes the issue for s390's use-cases. With that
pci_bus_read_config() becomes unused - and could be removed in further
refinements.
However, this probably breaks your dwc and cdns use-cases. I think,
with the accessor functions for dwc and cadence changed to follow the
{_byte|_word|_dword} naming pattern they could be used straight out of
PCI_FIND_NEXT_{EXT_}CAP, too. Then, dw_pcie_read_cfg() and
cdns_pcie_read_cfg become obsolete as well.
Thoughts?
Powered by blists - more mailing lists