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* [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value
@ 2020-08-01 11:24 Saheed O. Bolarinwa
  2020-08-01 11:24 ` [RFC PATCH 14/17] IB: " Saheed O. Bolarinwa
  2020-08-01 12:56 ` [RFC PATCH 00/17] " Borislav Petkov
  0 siblings, 2 replies; 9+ messages in thread
From: Saheed O. Bolarinwa @ 2020-08-01 11:24 UTC (permalink / raw)
  To: helgaas, Kalle Valo, David S. Miller, Jakub Kicinski,
	Wolfgang Grandegger, Marc Kleine-Budde, Miquel Raynal,
	Richard Weinberger, Vignesh Raghavendra, Joerg Roedel
  Cc: Saheed O. Bolarinwa, bjorn, skhan, linux-kernel-mentees,
	linux-pci, linux-kernel, linux-wireless, netdev, linux-mtd,
	iommu, linux-rdma, linux-ide, linux-i2c, linux-hwmon, dri-devel,
	intel-gfx, linux-gpio, linux-fpga, linux-edac, dmaengine,
	linux-crypto, linux-atm-general

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


^ permalink raw reply	[flat|nested] 9+ messages in thread

* [RFC PATCH 14/17] IB: Drop uses of pci_read_config_*() return value
  2020-08-01 11:24 [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value Saheed O. Bolarinwa
@ 2020-08-01 11:24 ` Saheed O. Bolarinwa
  2020-08-01 12:56 ` [RFC PATCH 00/17] " Borislav Petkov
  1 sibling, 0 replies; 9+ messages in thread
From: Saheed O. Bolarinwa @ 2020-08-01 11:24 UTC (permalink / raw)
  To: helgaas, Mike Marciniszyn, Dennis Dalessandro, Doug Ledford,
	Jason Gunthorpe
  Cc: Saheed O. Bolarinwa, bjorn, skhan, linux-kernel-mentees,
	linux-pci, linux-kernel, linux-rdma

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/infiniband/hw/hfi1/pcie.c         | 38 +++++++++++------------
 drivers/infiniband/hw/mthca/mthca_reset.c | 19 ++++++------
 2 files changed, 29 insertions(+), 28 deletions(-)

diff --git a/drivers/infiniband/hw/hfi1/pcie.c b/drivers/infiniband/hw/hfi1/pcie.c
index 1a6268d61977..11cf7dde873d 100644
--- a/drivers/infiniband/hw/hfi1/pcie.c
+++ b/drivers/infiniband/hw/hfi1/pcie.c
@@ -392,24 +392,24 @@ int restore_pci_variables(struct hfi1_devdata *dd)
 /* Save BARs and command to rewrite after device reset */
 int save_pci_variables(struct hfi1_devdata *dd)
 {
-	int ret = 0;
+	int ret = -ENODEV;
 
-	ret = pci_read_config_dword(dd->pcidev, PCI_BASE_ADDRESS_0,
+	pci_read_config_dword(dd->pcidev, PCI_BASE_ADDRESS_0,
 				    &dd->pcibar0);
-	if (ret)
+	if (dd->pcibar0 == (u32)~0)
 		goto error;
 
-	ret = pci_read_config_dword(dd->pcidev, PCI_BASE_ADDRESS_1,
+	pci_read_config_dword(dd->pcidev, PCI_BASE_ADDRESS_1,
 				    &dd->pcibar1);
-	if (ret)
+	if (dd->pcibar1 == (u32)~0)
 		goto error;
 
-	ret = pci_read_config_dword(dd->pcidev, PCI_ROM_ADDRESS, &dd->pci_rom);
-	if (ret)
+	pci_read_config_dword(dd->pcidev, PCI_ROM_ADDRESS, &dd->pci_rom);
+	if (dd->pci_rom == (u32)~0)
 		goto error;
 
-	ret = pci_read_config_word(dd->pcidev, PCI_COMMAND, &dd->pci_command);
-	if (ret)
+	pci_read_config_word(dd->pcidev, PCI_COMMAND, &dd->pci_command);
+	if (dd->pci_command == (u16)~0)
 		goto error;
 
 	ret = pcie_capability_read_word(dd->pcidev, PCI_EXP_DEVCTL,
@@ -427,14 +427,14 @@ int save_pci_variables(struct hfi1_devdata *dd)
 	if (ret)
 		goto error;
 
-	ret = pci_read_config_dword(dd->pcidev, PCI_CFG_MSIX0, &dd->pci_msix0);
-	if (ret)
+	pci_read_config_dword(dd->pcidev, PCI_CFG_MSIX0, &dd->pci_msix0);
+	if (dd->pci_command == (u32)~0)
 		goto error;
 
 	if (pci_find_ext_capability(dd->pcidev, PCI_EXT_CAP_ID_TPH)) {
-		ret = pci_read_config_dword(dd->pcidev, PCIE_CFG_TPH2,
+		pci_read_config_dword(dd->pcidev, PCIE_CFG_TPH2,
 					    &dd->pci_tph2);
-		if (ret)
+		if (dd->pci_tph2 == (u32)~0)
 			goto error;
 	}
 	return 0;
@@ -783,9 +783,9 @@ static int load_eq_table(struct hfi1_devdata *dd, const u8 eq[11][3], u8 fs,
 		pci_write_config_dword(pdev, PCIE_CFG_REG_PL102,
 				       eq_value(c_minus1, c0, c_plus1));
 		/* check if these coefficients violate EQ rules */
-		ret = pci_read_config_dword(dd->pcidev,
+		pci_read_config_dword(dd->pcidev,
 					    PCIE_CFG_REG_PL105, &violation);
-		if (ret) {
+		if (violation == (32)~0) {
 			dd_dev_err(dd, "Unable to read from PCI config\n");
 			hit_error = 1;
 			break;
@@ -1322,8 +1322,8 @@ int do_pcie_gen3_transition(struct hfi1_devdata *dd)
 	/* step 10: decide what to do next */
 
 	/* check if we can read PCI space */
-	ret = pci_read_config_word(dd->pcidev, PCI_VENDOR_ID, &vendor);
-	if (ret) {
+	pci_read_config_word(dd->pcidev, PCI_VENDOR_ID, &vendor);
+	if (vendor == (u16)~0) {
 		dd_dev_info(dd,
 			    "%s: read of VendorID failed after SBR, err %d\n",
 			    __func__, ret);
@@ -1376,8 +1376,8 @@ int do_pcie_gen3_transition(struct hfi1_devdata *dd)
 	setextled(dd, 0);
 
 	/* check for any per-lane errors */
-	ret = pci_read_config_dword(dd->pcidev, PCIE_CFG_SPCIE2, &reg32);
-	if (ret) {
+	pci_read_config_dword(dd->pcidev, PCIE_CFG_SPCIE2, &reg32);
+	if (reg32 == (u32)~0) {
 		dd_dev_err(dd, "Unable to read from PCI config\n");
 		return_error = 1;
 		goto done;
diff --git a/drivers/infiniband/hw/mthca/mthca_reset.c b/drivers/infiniband/hw/mthca/mthca_reset.c
index 2a6979e4ae1c..5f09d5312472 100644
--- a/drivers/infiniband/hw/mthca/mthca_reset.c
+++ b/drivers/infiniband/hw/mthca/mthca_reset.c
@@ -102,7 +102,10 @@ int mthca_reset(struct mthca_dev *mdev)
 	for (i = 0; i < 64; ++i) {
 		if (i == 22 || i == 23)
 			continue;
-		if (pci_read_config_dword(mdev->pdev, i * 4, hca_header + i)) {
+
+		pci_read_config_dword(mdev->pdev, i * 4,
+						hca_header + i);
+		if (*(hca_header + i) == (u32)~0) {
 			err = -ENODEV;
 			mthca_err(mdev, "Couldn't save HCA "
 				  "PCI header, aborting.\n");
@@ -123,7 +126,10 @@ int mthca_reset(struct mthca_dev *mdev)
 		for (i = 0; i < 64; ++i) {
 			if (i == 22 || i == 23)
 				continue;
-			if (pci_read_config_dword(bridge, i * 4, bridge_header + i)) {
+
+			pci_read_config_dword(bridge, i * 4,
+							bridge_header + i);
+			if (*(bridge_header + i) == (u32)~0) {
 				err = -ENODEV;
 				mthca_err(mdev, "Couldn't save HCA bridge "
 					  "PCI header, aborting.\n");
@@ -164,13 +170,8 @@ int mthca_reset(struct mthca_dev *mdev)
 		int c = 0;
 
 		for (c = 0; c < 100; ++c) {
-			if (pci_read_config_dword(bridge ? bridge : mdev->pdev, 0, &v)) {
-				err = -ENODEV;
-				mthca_err(mdev, "Couldn't access HCA after reset, "
-					  "aborting.\n");
-				goto free_bh;
-			}
-
+			pci_read_config_dword(bridge ? bridge : mdev->pdev, 0,
+									&v);
 			if (v != 0xffffffff)
 				goto good;
 
-- 
2.18.4


^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value
  2020-08-01 11:24 [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value Saheed O. Bolarinwa
  2020-08-01 11:24 ` [RFC PATCH 14/17] IB: " Saheed O. Bolarinwa
@ 2020-08-01 12:56 ` Borislav Petkov
  2020-08-02 14:53   ` Tom Rix
  2020-08-02 17:28   ` Saheed Bolarinwa
  1 sibling, 2 replies; 9+ messages in thread
From: Borislav Petkov @ 2020-08-01 12:56 UTC (permalink / raw)
  To: Saheed O. Bolarinwa
  Cc: helgaas, Kalle Valo, David S. Miller, Jakub Kicinski,
	Wolfgang Grandegger, Marc Kleine-Budde, Miquel Raynal,
	Richard Weinberger, Vignesh Raghavendra, Joerg Roedel, bjorn,
	skhan, linux-kernel-mentees, linux-pci, linux-kernel,
	linux-wireless, netdev, linux-mtd, iommu, linux-rdma, linux-ide,
	linux-i2c, linux-hwmon, dri-devel, intel-gfx, linux-gpio,
	linux-fpga, linux-edac, dmaengine, linux-crypto,
	linux-atm-general

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

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value
  2020-08-01 12:56 ` [RFC PATCH 00/17] " Borislav Petkov
@ 2020-08-02 14:53   ` Tom Rix
  2020-08-02 17:28   ` Saheed Bolarinwa
  1 sibling, 0 replies; 9+ messages in thread
From: Tom Rix @ 2020-08-02 14:53 UTC (permalink / raw)
  To: Borislav Petkov, Saheed O. Bolarinwa
  Cc: helgaas, Kalle Valo, David S. Miller, Jakub Kicinski,
	Wolfgang Grandegger, Marc Kleine-Budde, Miquel Raynal,
	Richard Weinberger, Vignesh Raghavendra, Joerg Roedel, bjorn,
	skhan, linux-kernel-mentees, linux-pci, linux-kernel,
	linux-wireless, netdev, linux-mtd, iommu, linux-rdma, linux-ide,
	linux-i2c, linux-hwmon, dri-devel, intel-gfx, linux-gpio,
	linux-fpga, linux-edac, dmaengine, linux-crypto,
	linux-atm-general


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


^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value
  2020-08-01 12:56 ` [RFC PATCH 00/17] " Borislav Petkov
  2020-08-02 14:53   ` Tom Rix
@ 2020-08-02 17:28   ` Saheed Bolarinwa
  2020-08-02 18:46     ` Borislav Petkov
  1 sibling, 1 reply; 9+ messages in thread
From: Saheed Bolarinwa @ 2020-08-02 17:28 UTC (permalink / raw)
  To: Borislav Petkov, trix
  Cc: helgaas, Kalle Valo, David S. Miller, Jakub Kicinski,
	Wolfgang Grandegger, Marc Kleine-Budde, Miquel Raynal,
	Richard Weinberger, Vignesh Raghavendra, Joerg Roedel, bjorn,
	skhan, linux-kernel-mentees, linux-pci, linux-kernel,
	linux-wireless, netdev, linux-mtd, iommu, linux-rdma, linux-ide,
	linux-i2c, linux-hwmon, dri-devel, intel-gfx, linux-gpio,
	linux-fpga, linux-edac, dmaengine, linux-crypto,
	linux-atm-general


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


^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value
  2020-08-02 17:28   ` Saheed Bolarinwa
@ 2020-08-02 18:46     ` Borislav Petkov
  2020-08-02 19:14       ` Bjorn Helgaas
  0 siblings, 1 reply; 9+ messages in thread
From: Borislav Petkov @ 2020-08-02 18:46 UTC (permalink / raw)
  To: Saheed Bolarinwa
  Cc: trix, helgaas, Kalle Valo, David S. Miller, Jakub Kicinski,
	Wolfgang Grandegger, Marc Kleine-Budde, Miquel Raynal,
	Richard Weinberger, Vignesh Raghavendra, Joerg Roedel, bjorn,
	skhan, linux-kernel-mentees, linux-pci, linux-kernel,
	linux-wireless, netdev, linux-mtd, iommu, linux-rdma, linux-ide,
	linux-i2c, linux-hwmon, dri-devel, intel-gfx, linux-gpio,
	linux-fpga, linux-edac, dmaengine, linux-crypto,
	linux-atm-general

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

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value
  2020-08-02 18:46     ` Borislav Petkov
@ 2020-08-02 19:14       ` Bjorn Helgaas
  2020-08-02 20:18         ` Borislav Petkov
  2020-08-03  6:56         ` Christoph Hellwig
  0 siblings, 2 replies; 9+ messages in thread
From: Bjorn Helgaas @ 2020-08-02 19:14 UTC (permalink / raw)
  To: Borislav Petkov
  Cc: Saheed Bolarinwa, trix, Kalle Valo, David S. Miller,
	Jakub Kicinski, Wolfgang Grandegger, Marc Kleine-Budde,
	Miquel Raynal, Richard Weinberger, Vignesh Raghavendra,
	Joerg Roedel, bjorn, skhan, linux-kernel-mentees, linux-pci,
	linux-kernel, linux-wireless, netdev, linux-mtd, iommu,
	linux-rdma, linux-ide, linux-i2c, linux-hwmon, dri-devel,
	intel-gfx, linux-gpio, linux-fpga, linux-edac, dmaengine,
	linux-crypto, linux-atm-general

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

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value
  2020-08-02 19:14       ` Bjorn Helgaas
@ 2020-08-02 20:18         ` Borislav Petkov
  2020-08-03  6:56         ` Christoph Hellwig
  1 sibling, 0 replies; 9+ messages in thread
From: Borislav Petkov @ 2020-08-02 20:18 UTC (permalink / raw)
  To: Bjorn Helgaas
  Cc: Saheed Bolarinwa, trix, Kalle Valo, David S. Miller,
	Jakub Kicinski, Wolfgang Grandegger, Marc Kleine-Budde,
	Miquel Raynal, Richard Weinberger, Vignesh Raghavendra,
	Joerg Roedel, bjorn, skhan, linux-kernel-mentees, linux-pci,
	linux-kernel, linux-wireless, netdev, linux-mtd, iommu,
	linux-rdma, linux-ide, linux-i2c, linux-hwmon, dri-devel,
	intel-gfx, linux-gpio, linux-fpga, linux-edac, dmaengine,
	linux-crypto, linux-atm-general

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

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value
  2020-08-02 19:14       ` Bjorn Helgaas
  2020-08-02 20:18         ` Borislav Petkov
@ 2020-08-03  6:56         ` Christoph Hellwig
  1 sibling, 0 replies; 9+ messages in thread
From: Christoph Hellwig @ 2020-08-03  6:56 UTC (permalink / raw)
  To: Bjorn Helgaas
  Cc: Borislav Petkov, Saheed Bolarinwa, trix, Kalle Valo,
	David S. Miller, Jakub Kicinski, Wolfgang Grandegger,
	Marc Kleine-Budde, Miquel Raynal, Richard Weinberger,
	Vignesh Raghavendra, Joerg Roedel, bjorn, skhan,
	linux-kernel-mentees, linux-pci, linux-kernel, linux-wireless,
	netdev, linux-mtd, iommu, linux-rdma, linux-ide, linux-i2c,
	linux-hwmon, dri-devel, intel-gfx, linux-gpio, linux-fpga,
	linux-edac, dmaengine, linux-crypto, linux-atm-general

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)

^ permalink raw reply	[flat|nested] 9+ messages in thread

end of thread, back to index

Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-08-01 11:24 [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value Saheed O. Bolarinwa
2020-08-01 11:24 ` [RFC PATCH 14/17] IB: " Saheed O. Bolarinwa
2020-08-01 12:56 ` [RFC PATCH 00/17] " Borislav Petkov
2020-08-02 14:53   ` Tom Rix
2020-08-02 17:28   ` Saheed Bolarinwa
2020-08-02 18:46     ` Borislav Petkov
2020-08-02 19:14       ` Bjorn Helgaas
2020-08-02 20:18         ` Borislav Petkov
2020-08-03  6:56         ` Christoph Hellwig

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