[RFC PATCH 00/17] Drop uses of pci_read_config_*() return value

[RFC PATCH 00/17] Drop uses of pci_read_config_*() return value

[Saheed O. Bolarinwa]

The return value of pci_read_config_*() may not indicate a device error.
However, the value read by these functions is more likely to indicate
this kind of error. This presents two overlapping ways of reporting
errors and complicates error checking.

It is possible to move to one single way of checking for error if the 
dependencies on the return value of these functions are removed, then it
can later be made to return void.

Remove all uses of the return value of pci_read_config_*().
Check the actual value read for ~0. In this case, ~0 is an invalid value
thus it indicates some kind of error.

In some cases it madkes sence to make the calling function return void
without causing any bug. Future callers can use the value obtained from
these functions for validation. This case pertain to cs5536_read() and 
edac_pci_read_dword()

MERGE:
There is no dependency.
Merge individually

Saheed O. Bolarinwa (17):
  ata: Drop uses of pci_read_config_*() return value
  atm: Drop uses of pci_read_config_*() return value
  bcma: Drop uses of pci_read_config_*() return value
  hwrng: Drop uses of pci_read_config_*() return value
  dmaengine: ioat: Drop uses of pci_read_config_*() return value
  edac: Drop uses of pci_read_config_*() return value
  fpga: altera-cvp: Drop uses of pci_read_config_*() return value
  gpio: Drop uses of pci_read_config_*() return value
  drm/i915/vga: Drop uses of pci_read_config_*() return value
  hwmon: Drop uses of pci_read_config_*() return value
  intel_th: pci: Drop uses of pci_read_config_*() return value
  i2c: Drop uses of pci_read_config_*() return value
  ide: Drop uses of pci_read_config_*() return value
  IB: Drop uses of pci_read_config_*() return value
  iommu/vt-d: Drop uses of pci_read_config_*() return value
  mtd: Drop uses of pci_read_config_*() return value
  net: Drop uses of pci_read_config_*() return value

 drivers/ata/pata_cs5536.c                     |  6 +--
 drivers/ata/pata_rz1000.c                     |  3 +-
 drivers/atm/eni.c                             |  3 +-
 drivers/atm/he.c                              | 12 +++--
 drivers/atm/idt77252.c                        |  9 ++--
 drivers/atm/iphase.c                          | 46 ++++++++++---------
 drivers/atm/lanai.c                           |  4 +-
 drivers/atm/nicstar.c                         |  3 +-
 drivers/atm/zatm.c                            |  9 ++--
 drivers/bcma/host_pci.c                       |  6 ++-
 drivers/char/hw_random/amd-rng.c              |  6 +--
 drivers/dma/ioat/dma.c                        |  6 +--
 drivers/edac/amd64_edac.c                     |  8 ++--
 drivers/edac/amd8111_edac.c                   | 16 ++-----
 drivers/edac/amd8131_edac.c                   |  6 +--
 drivers/edac/i82443bxgx_edac.c                |  3 +-
 drivers/edac/sb_edac.c                        | 12 +++--
 drivers/edac/skx_common.c                     | 18 +++++---
 drivers/fpga/altera-cvp.c                     |  8 ++--
 drivers/gpio/gpio-amd8111.c                   |  7 ++-
 drivers/gpio/gpio-rdc321x.c                   | 21 +++++----
 drivers/gpu/drm/i915/display/intel_vga.c      |  3 +-
 drivers/hwmon/i5k_amb.c                       | 12 +++--
 drivers/hwmon/vt8231.c                        |  8 ++--
 drivers/hwtracing/intel_th/pci.c              | 12 ++---
 drivers/i2c/busses/i2c-ali15x3.c              |  6 ++-
 drivers/i2c/busses/i2c-elektor.c              |  3 +-
 drivers/i2c/busses/i2c-nforce2.c              |  4 +-
 drivers/i2c/busses/i2c-sis5595.c              | 17 ++++---
 drivers/i2c/busses/i2c-sis630.c               |  7 +--
 drivers/i2c/busses/i2c-viapro.c               | 11 +++--
 drivers/ide/cs5536.c                          |  6 +--
 drivers/ide/rz1000.c                          |  3 +-
 drivers/ide/setup-pci.c                       | 26 +++++++----
 drivers/infiniband/hw/hfi1/pcie.c             | 38 +++++++--------
 drivers/infiniband/hw/mthca/mthca_reset.c     | 19 ++++----
 drivers/iommu/intel/iommu.c                   |  6 ++-
 drivers/mtd/maps/ichxrom.c                    |  4 +-
 drivers/net/can/peak_canfd/peak_pciefd_main.c |  6 ++-
 drivers/net/can/sja1000/peak_pci.c            |  6 ++-
 drivers/net/ethernet/agere/et131x.c           | 11 +++--
 .../ethernet/broadcom/bnx2x/bnx2x_ethtool.c   |  5 +-
 .../cavium/liquidio/cn23xx_pf_device.c        |  4 +-
 drivers/net/ethernet/marvell/sky2.c           |  5 +-
 drivers/net/ethernet/mellanox/mlx4/catas.c    |  7 +--
 drivers/net/ethernet/mellanox/mlx4/reset.c    | 10 ++--
 .../net/ethernet/myricom/myri10ge/myri10ge.c  |  4 +-
 drivers/net/wan/farsync.c                     |  5 +-
 .../broadcom/brcm80211/brcmfmac/pcie.c        |  4 +-
 .../net/wireless/intel/iwlwifi/pcie/trans.c   | 15 ++++--
 50 files changed, 270 insertions(+), 209 deletions(-)

-- 
2.18.4

[RFC PATCH 08/17] gpio: Drop uses of pci_read_config_*() return value

[Saheed O. Bolarinwa]

The return value of pci_read_config_*() may not indicate a device error.
However, the value read by these functions is more likely to indicate
this kind of error. This presents two overlapping ways of reporting
errors and complicates error checking.

It is possible to move to one single way of checking for error if the
dependency on the return value of these functions is removed, then it
can later be made to return void.

Remove all uses of the return value of pci_read_config_*().
Check the actual value read for ~0. In this case, ~0 is an invalid
value thus it indicates some kind of error.

Suggested-by: Bjorn Helgaas <bjorn@helgaas.com>
Signed-off-by: Saheed O. Bolarinwa <refactormyself@gmail.com>
---
 drivers/gpio/gpio-amd8111.c |  7 +++++--
 drivers/gpio/gpio-rdc321x.c | 21 ++++++++++++---------
 2 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/drivers/gpio/gpio-amd8111.c b/drivers/gpio/gpio-amd8111.c
index fdcebe59510d..7b9882380cbc 100644
--- a/drivers/gpio/gpio-amd8111.c
+++ b/drivers/gpio/gpio-amd8111.c
@@ -198,9 +198,12 @@ static int __init amd_gpio_init(void)
 	goto out;
 
 found:
-	err = pci_read_config_dword(pdev, 0x58, &gp.pmbase);
-	if (err)
+	pci_read_config_dword(pdev, 0x58, &gp.pmbase);
+	if (gp.pmbase == (u32)~0) {
+		err = -ENODEV;
 		goto out;
+	}
+
 	err = -EIO;
 	gp.pmbase &= 0x0000FF00;
 	if (gp.pmbase == 0)
diff --git a/drivers/gpio/gpio-rdc321x.c b/drivers/gpio/gpio-rdc321x.c
index 01ed2517e9fd..03f1ff07b844 100644
--- a/drivers/gpio/gpio-rdc321x.c
+++ b/drivers/gpio/gpio-rdc321x.c
@@ -85,10 +85,13 @@ static int rdc_gpio_config(struct gpio_chip *chip,
 	gpch = gpiochip_get_data(chip);
 
 	spin_lock(&gpch->lock);
-	err = pci_read_config_dword(gpch->sb_pdev, gpio < 32 ?
-			gpch->reg1_ctrl_base : gpch->reg2_ctrl_base, &reg);
-	if (err)
+	pci_read_config_dword(gpch->sb_pdev,
+				(gpio < 32) ? gpch->reg1_ctrl_base
+					: gpch->reg2_ctrl_base, &reg);
+	if (reg == (u32)~0) {
+		err = -ENODEV;
 		goto unlock;
+	}
 
 	reg |= 1 << (gpio & 0x1f);
 
@@ -166,17 +169,17 @@ static int rdc321x_gpio_probe(struct platform_device *pdev)
 	/* This might not be, what others (BIOS, bootloader, etc.)
 	   wrote to these registers before, but it's a good guess. Still
 	   better than just using 0xffffffff. */
-	err = pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
+	pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
 					rdc321x_gpio_dev->reg1_data_base,
 					&rdc321x_gpio_dev->data_reg[0]);
-	if (err)
-		return err;
+	if (rdc321x_gpio_dev->data_reg[0] == (u32)~0)
+		return -ENODEV;
 
-	err = pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
+	pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
 					rdc321x_gpio_dev->reg2_data_base,
 					&rdc321x_gpio_dev->data_reg[1]);
-	if (err)
-		return err;
+	if (rdc321x_gpio_dev->data_reg[1] == (u32)~0)
+		return -ENODEV;
 
 	dev_info(&pdev->dev, "registering %d GPIOs\n",
 					rdc321x_gpio_dev->chip.ngpio);
-- 
2.18.4

Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value

[Borislav Petkov]

On Sat, Aug 01, 2020 at 01:24:29PM +0200, Saheed O. Bolarinwa wrote:
> The return value of pci_read_config_*() may not indicate a device error.
> However, the value read by these functions is more likely to indicate
> this kind of error. This presents two overlapping ways of reporting
> errors and complicates error checking.

So why isn't the *value check done in the pci_read_config_* functions
instead of touching gazillion callers?

For example, pci_conf{1,2}_read() could check whether the u32 *value it
just read depending on the access method, whether that value is ~0 and
return proper PCIBIOS_ error in that case.

The check you're replicating

	if (val32 == (u32)~0)

everywhere, instead, is just ugly and tests a naked value ~0 which
doesn't mean anything...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value

[Tom Rix]

On 8/1/20 5:56 AM, Borislav Petkov wrote:
> On Sat, Aug 01, 2020 at 01:24:29PM +0200, Saheed O. Bolarinwa wrote:
>> The return value of pci_read_config_*() may not indicate a device error.
>> However, the value read by these functions is more likely to indicate
>> this kind of error. This presents two overlapping ways of reporting
>> errors and complicates error checking.
> So why isn't the *value check done in the pci_read_config_* functions
> instead of touching gazillion callers?
>
> For example, pci_conf{1,2}_read() could check whether the u32 *value it
> just read depending on the access method, whether that value is ~0 and
> return proper PCIBIOS_ error in that case.
>
> The check you're replicating
>
> 	if (val32 == (u32)~0)
>
> everywhere, instead, is just ugly and tests a naked value ~0 which
> doesn't mean anything...
>
I agree, if there is a change, it should be in the pci_read_* functions.

Anything returning void should not fail and likely future users of the proposed change will not do the extra checks.

Tom

Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value

[Saheed Bolarinwa]

On 8/1/20 2:56 PM, Borislav Petkov wrote:
> On Sat, Aug 01, 2020 at 01:24:29PM +0200, Saheed O. Bolarinwa wrote:
>> The return value of pci_read_config_*() may not indicate a device error.
>> However, the value read by these functions is more likely to indicate
>> this kind of error. This presents two overlapping ways of reporting
>> errors and complicates error checking.
> So why isn't the *value check done in the pci_read_config_* functions
> instead of touching gazillion callers?
Because the value ~0 has a meaning to some drivers and only
drivers have this knowledge. For those cases more checks will
be needed to ensure that it is an error that has actually
happened.
> For example, pci_conf{1,2}_read() could check whether the u32 *value it
> just read depending on the access method, whether that value is ~0 and
> return proper PCIBIOS_ error in that case.

The primary goal is to make pci_config_read*() return void, so
that there is *only* one way to check for error i.e. through the
obtained value.
Again, only the drivers can determine if ~0 is a valid value. This
information is not available inside pci_config_read*().

- Saheed

Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value

[Borislav Petkov]

On Sun, Aug 02, 2020 at 07:28:00PM +0200, Saheed Bolarinwa wrote:
> Because the value ~0 has a meaning to some drivers and only

No, ~0 means that the PCI read failed. For *every* PCI device I know.

Here's me reading from 0xf0 offset of my hostbridge:

# setpci -s 00:00.0 0xf0.l
01000000

That device doesn't have extended config space, so the last valid byte
is 0xff. Let's read beyond that:

# setpci -s 00:00.0 0x100.l
ffffffff

> Again, only the drivers can determine if ~0 is a valid value. This
> information is not available inside pci_config_read*().

Of course it is.

*every* change you've done in 6/17 - this is the only patch I have
received - checks for == ~0. So that check can just as well be moved
inside pci_config_read_*().

Here's how one could do it:

#define PCI_OP_READ(size, type, len) \
int noinline pci_bus_read_config_##size \
	(struct pci_bus *bus, unsigned int devfn, int pos, type *value)	\
{									\
	int res;							\
	unsigned long flags;						\
	u32 data = 0;							\
	if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER;	\
	pci_lock_config(flags);						\
	res = bus->ops->read(bus, devfn, pos, len, &data);		\

	/* Check we actually read something which is not all 1s.*/
	if (data == ~0)
		return PCIBIOS_READ_FAILED;

	*value = (type)data;						\
	pci_unlock_config(flags);					\
	return res;							\
}

Also, I'd prefer a function to *not* return void but return either
an error or success. In the success case, the @value argument can be
consumed by the caller and otherwise not.

In any case, that change is a step in the wrong direction and I don't
like it, sorry.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value

[Bjorn Helgaas]

On Sun, Aug 02, 2020 at 08:46:48PM +0200, Borislav Petkov wrote:
> On Sun, Aug 02, 2020 at 07:28:00PM +0200, Saheed Bolarinwa wrote:
> > Because the value ~0 has a meaning to some drivers and only
> 
> No, ~0 means that the PCI read failed. For *every* PCI device I know.

Wait, I'm not convinced yet.  I know that if a PCI read fails, you
normally get ~0 data because the host bridge fabricates it to complete
the CPU load.

But what guarantees that a PCI config register cannot contain ~0?
If there's something about that in the spec I'd love to know where it
is because it would simplify a lot of things.

I don't think we should merge any of these patches as-is.  If we *do*
want to go this direction, we at least need some kind of macro or
function that tests for ~0 so we have a clue about what's happening
and can grep for it.

Bjorn

Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value

[Borislav Petkov]

On Sun, Aug 02, 2020 at 02:14:06PM -0500, Bjorn Helgaas wrote:
> Wait, I'm not convinced yet.  I know that if a PCI read fails, you
> normally get ~0 data because the host bridge fabricates it to complete
> the CPU load.
> 
> But what guarantees that a PCI config register cannot contain ~0?

Well, I don't think you can differentiate that case, right?

I guess this is where the driver knowledge comes into play: if the read
returns ~0, the pci_read_config* should probably return in that case
something like:

	PCIBIOS_READ_MAYBE_FAILED

to denote it is all 1s and then the caller should be able to determine,
based on any of domain:bus:slot.func and whatever else the driver knows
about its hardware, whether the 1s are a valid value or an error.
Hopefully.

Or something better of which I cannot think of right now...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value

[Christoph Hellwig]

On Sun, Aug 02, 2020 at 02:14:06PM -0500, Bjorn Helgaas wrote:
> But what guarantees that a PCI config register cannot contain ~0?
> If there's something about that in the spec I'd love to know where it
> is because it would simplify a lot of things.

There isn't.  An we even have cases like the NVMe controller memory
buffer and persistent memory region, which are BARs that store
abritrary values for later retreival, so it can't.  (now those
features have a major issue with error detection, but that is another
issue)

Re: [RFC PATCH 08/17] gpio: Drop uses of pci_read_config_*() return value

[Bartosz Golaszewski]

On Sat, Aug 1, 2020 at 2:24 PM Saheed O. Bolarinwa
<refactormyself@gmail.com> wrote:
>
> The return value of pci_read_config_*() may not indicate a device error.
> However, the value read by these functions is more likely to indicate
> this kind of error. This presents two overlapping ways of reporting
> errors and complicates error checking.
>
> It is possible to move to one single way of checking for error if the
> dependency on the return value of these functions is removed, then it
> can later be made to return void.
>
> Remove all uses of the return value of pci_read_config_*().
> Check the actual value read for ~0. In this case, ~0 is an invalid
> value thus it indicates some kind of error.
>
> Suggested-by: Bjorn Helgaas <bjorn@helgaas.com>
> Signed-off-by: Saheed O. Bolarinwa <refactormyself@gmail.com>
> ---
>  drivers/gpio/gpio-amd8111.c |  7 +++++--
>  drivers/gpio/gpio-rdc321x.c | 21 ++++++++++++---------
>  2 files changed, 17 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpio/gpio-amd8111.c b/drivers/gpio/gpio-amd8111.c
> index fdcebe59510d..7b9882380cbc 100644
> --- a/drivers/gpio/gpio-amd8111.c
> +++ b/drivers/gpio/gpio-amd8111.c
> @@ -198,9 +198,12 @@ static int __init amd_gpio_init(void)
>         goto out;
>
>  found:
> -       err = pci_read_config_dword(pdev, 0x58, &gp.pmbase);
> -       if (err)
> +       pci_read_config_dword(pdev, 0x58, &gp.pmbase);
> +       if (gp.pmbase == (u32)~0) {
> +               err = -ENODEV;
>                 goto out;
> +       }
> +
>         err = -EIO;
>         gp.pmbase &= 0x0000FF00;
>         if (gp.pmbase == 0)
> diff --git a/drivers/gpio/gpio-rdc321x.c b/drivers/gpio/gpio-rdc321x.c
> index 01ed2517e9fd..03f1ff07b844 100644
> --- a/drivers/gpio/gpio-rdc321x.c
> +++ b/drivers/gpio/gpio-rdc321x.c
> @@ -85,10 +85,13 @@ static int rdc_gpio_config(struct gpio_chip *chip,
>         gpch = gpiochip_get_data(chip);
>
>         spin_lock(&gpch->lock);
> -       err = pci_read_config_dword(gpch->sb_pdev, gpio < 32 ?
> -                       gpch->reg1_ctrl_base : gpch->reg2_ctrl_base, &reg);
> -       if (err)
> +       pci_read_config_dword(gpch->sb_pdev,
> +                               (gpio < 32) ? gpch->reg1_ctrl_base
> +                                       : gpch->reg2_ctrl_base, &reg);
> +       if (reg == (u32)~0) {
> +               err = -ENODEV;
>                 goto unlock;
> +       }
>
>         reg |= 1 << (gpio & 0x1f);
>
> @@ -166,17 +169,17 @@ static int rdc321x_gpio_probe(struct platform_device *pdev)
>         /* This might not be, what others (BIOS, bootloader, etc.)
>            wrote to these registers before, but it's a good guess. Still
>            better than just using 0xffffffff. */
> -       err = pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
> +       pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
>                                         rdc321x_gpio_dev->reg1_data_base,
>                                         &rdc321x_gpio_dev->data_reg[0]);
> -       if (err)
> -               return err;
> +       if (rdc321x_gpio_dev->data_reg[0] == (u32)~0)
> +               return -ENODEV;
>
> -       err = pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
> +       pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
>                                         rdc321x_gpio_dev->reg2_data_base,
>                                         &rdc321x_gpio_dev->data_reg[1]);
> -       if (err)
> -               return err;
> +       if (rdc321x_gpio_dev->data_reg[1] == (u32)~0)
> +               return -ENODEV;
>
>         dev_info(&pdev->dev, "registering %d GPIOs\n",
>                                         rdc321x_gpio_dev->chip.ngpio);
> --
> 2.18.4
>

Bjorn,

I don't know the pci sub-system at all. Does this look good to you?

Bartosz

Re: [RFC PATCH 08/17] gpio: Drop uses of pci_read_config_*() return value

[Bjorn Helgaas]

On Tue, Aug 18, 2020 at 09:59:50PM +0200, Bartosz Golaszewski wrote:
> On Sat, Aug 1, 2020 at 2:24 PM Saheed O. Bolarinwa
> <refactormyself@gmail.com> wrote:
> >
> > The return value of pci_read_config_*() may not indicate a device error.
> > However, the value read by these functions is more likely to indicate
> > this kind of error. This presents two overlapping ways of reporting
> > errors and complicates error checking.
> >
> > It is possible to move to one single way of checking for error if the
> > dependency on the return value of these functions is removed, then it
> > can later be made to return void.
> >
> > Remove all uses of the return value of pci_read_config_*().
> > Check the actual value read for ~0. In this case, ~0 is an invalid
> > value thus it indicates some kind of error.
> >
> > Suggested-by: Bjorn Helgaas <bjorn@helgaas.com>
> > Signed-off-by: Saheed O. Bolarinwa <refactormyself@gmail.com>
> > ---
> >  drivers/gpio/gpio-amd8111.c |  7 +++++--
> >  drivers/gpio/gpio-rdc321x.c | 21 ++++++++++++---------
> >  2 files changed, 17 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/gpio/gpio-amd8111.c b/drivers/gpio/gpio-amd8111.c
> > index fdcebe59510d..7b9882380cbc 100644
> > --- a/drivers/gpio/gpio-amd8111.c
> > +++ b/drivers/gpio/gpio-amd8111.c
> > @@ -198,9 +198,12 @@ static int __init amd_gpio_init(void)
> >         goto out;
> >
> >  found:
> > -       err = pci_read_config_dword(pdev, 0x58, &gp.pmbase);
> > -       if (err)
> > +       pci_read_config_dword(pdev, 0x58, &gp.pmbase);
> > +       if (gp.pmbase == (u32)~0) {
> > +               err = -ENODEV;
> >                 goto out;
> > +       }
> > +
> >         err = -EIO;
> >         gp.pmbase &= 0x0000FF00;
> >         if (gp.pmbase == 0)
> > diff --git a/drivers/gpio/gpio-rdc321x.c b/drivers/gpio/gpio-rdc321x.c
> > index 01ed2517e9fd..03f1ff07b844 100644
> > --- a/drivers/gpio/gpio-rdc321x.c
> > +++ b/drivers/gpio/gpio-rdc321x.c
> > @@ -85,10 +85,13 @@ static int rdc_gpio_config(struct gpio_chip *chip,
> >         gpch = gpiochip_get_data(chip);
> >
> >         spin_lock(&gpch->lock);
> > -       err = pci_read_config_dword(gpch->sb_pdev, gpio < 32 ?
> > -                       gpch->reg1_ctrl_base : gpch->reg2_ctrl_base, &reg);
> > -       if (err)
> > +       pci_read_config_dword(gpch->sb_pdev,
> > +                               (gpio < 32) ? gpch->reg1_ctrl_base
> > +                                       : gpch->reg2_ctrl_base, &reg);
> > +       if (reg == (u32)~0) {
> > +               err = -ENODEV;
> >                 goto unlock;
> > +       }
> >
> >         reg |= 1 << (gpio & 0x1f);
> >
> > @@ -166,17 +169,17 @@ static int rdc321x_gpio_probe(struct platform_device *pdev)
> >         /* This might not be, what others (BIOS, bootloader, etc.)
> >            wrote to these registers before, but it's a good guess. Still
> >            better than just using 0xffffffff. */
> > -       err = pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
> > +       pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
> >                                         rdc321x_gpio_dev->reg1_data_base,
> >                                         &rdc321x_gpio_dev->data_reg[0]);
> > -       if (err)
> > -               return err;
> > +       if (rdc321x_gpio_dev->data_reg[0] == (u32)~0)
> > +               return -ENODEV;
> >
> > -       err = pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
> > +       pci_read_config_dword(rdc321x_gpio_dev->sb_pdev,
> >                                         rdc321x_gpio_dev->reg2_data_base,
> >                                         &rdc321x_gpio_dev->data_reg[1]);
> > -       if (err)
> > -               return err;
> > +       if (rdc321x_gpio_dev->data_reg[1] == (u32)~0)
> > +               return -ENODEV;
> >
> >         dev_info(&pdev->dev, "registering %d GPIOs\n",
> >                                         rdc321x_gpio_dev->chip.ngpio);
> > --
> > 2.18.4
> >
> 
> Bjorn,
> 
> I don't know the pci sub-system at all. Does this look good to you?

I wouldn't apply this at this point.  It's definitely true that when
pci_read_config_dword() returns an error, it's likely an alignment
problem or some other programming error, not an actual PCI error.

If an actual PCI error occurs (device failed to respond, transaction
failed because of noise or electrical issue, etc),
pci_read_config_dword() will *not* return an error; the data it reads,
e.g., rdc321x_gpio_dev->data_reg[1], will be ~0.

So with the current pci_read_config_dword() implementation, we really
need to test *both* the return value and the read data to be
completely, obsessively correct.  But that's really not practical,
hence this RFC patch where we're considering getting rid of the return
value and just making it set the read data to ~0 for all errors.

We might still get there someday, but we don't yet set the read data
to ~0 on all errors, and if/when we do that, we should have some sort
of descriptive macro that we can grep for instead of open-coding "~0"
everywhere.

Bjorn