On Monday 11 October 2021 23:55:35 Naveen Naidu wrote:
> On 11/10, Pali Rohár wrote:
> > On Monday 11 October 2021 23:26:33 Naveen Naidu wrote:
> > > An MMIO read from a PCI device that doesn't exist or doesn't respond
> > > causes a PCI error. There's no real data to return to satisfy the
> > > CPU read, so most hardware fabricates ~0 data.
> > >
> > > Use SET_PCI_ERROR_RESPONSE() to set the error response, when a faulty
> > > read occurs.
> > >
> > > This helps unify PCI error response checking and make error check
> > > consistent and easier to find.
> > >
> > > Compile tested only.
> > >
> > > Signed-off-by: Naveen Naidu <naveennaidu479@xxxxxxxxx>
> > > ---
> > > drivers/pci/controller/pci-aardvark.c | 8 ++++----
> > > 1 file changed, 4 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > > index 596ebcfcc82d..dc2f820ef55f 100644
> > > --- a/drivers/pci/controller/pci-aardvark.c
> > > +++ b/drivers/pci/controller/pci-aardvark.c
> > > @@ -894,7 +894,7 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
> > > int ret;
> > >
> > > if (!advk_pcie_valid_device(pcie, bus, devfn)) {
> > > - *val = 0xffffffff;
> > > + SET_PCI_ERROR_RESPONSE(val);
> >
> > Hello! Now I'm looking at this macro, and should not it depends on
> > "size" argument? If doing 8-bit or 16-bit read operation then should not
> > it rather sets only low 8 bits or low 16 bits to ones?
> >
>
> Hello o/, Thank you for the review.
>
> Yes! you are right that it should indeed depend on the "size" argument.
> And that is what the SET_PCI_ERROR_RESPONSE macro does. The macro is
> defined as:
>
> #define PCI_ERROR_RESPONSE (~0ULL)
> #define SET_PCI_ERROR_RESPONSE(val) (*val = ((typeof(*val))PCI_ERROR_RESPONSE))
>
> The macro was part of "Patch 1/22" and is present here [1]. Apologies if
> I added the receipient incorrectly.
>
> [1]:
> https://lore.kernel.org/linux-pci/d8e423386aad3d78bca575a7521b138508638e3b.1633972263.git.naveennaidu479@xxxxxxxxx/T/#m37295a0dcfe0d7e0f67efce3633efd7b891949c4
>
> IIUC, the typeof(*val) helps in setting the value according to the size
> of the argument.
>
> Please let me know if my understanding is wrong.
Hello! I mean "size" function argument which is passed as variable.
Function itself is declared as:
static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn, int where, int size, u32 *val);
And in "size" argument is stored number of bytes, kind of read operation
(read byte, read word, read dword). In *val is then stored read value.
For byte operation, just low 8 bits in *val variable are set.
Because *val is u32 it means that typeof(*val) is always 4 independently
of the "size" argument.
For example other project U-Boot has also pci-aardvark.c driver and
U-Boot has for (probably same) purpose pci_get_ff() macro, see:
https://source.denx.de/u-boot/u-boot/-/blob/v2021.10/drivers/pci/pci-aardvark.c#L367
I'm not saying if current approach to always sets 0xffffffff
(independently of "size" argument) is correct or not as I do not know
it too! I'm just giving example that this PCI code has very similar
implementation of other project (U-Boot) which sets number of ones based
on the size argument.
So probably something for other people to decide.
Anyway, I very like this your idea to have a macro which purpose is to
explicitly indicate error during config read operation! And to unify all
drivers to use same style for signalling config read error.
> > > return PCIBIOS_DEVICE_NOT_FOUND;
> > > }
> > >
> > > @@ -920,7 +920,7 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
> > > *val = CFG_RD_CRS_VAL;
> > > return PCIBIOS_SUCCESSFUL;
> > > }
> > > - *val = 0xffffffff;
> > > + SET_PCI_ERROR_RESPONSE(val);
> > > return PCIBIOS_SET_FAILED;
> > > }
> > >
> > > @@ -955,14 +955,14 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
> > > *val = CFG_RD_CRS_VAL;
> > > return PCIBIOS_SUCCESSFUL;
> > > }
> > > - *val = 0xffffffff;
> > > + SET_PCI_ERROR_RESPONSE(val);
> > > return PCIBIOS_SET_FAILED;
> > > }
> > >
> > > /* Check PIO status and get the read result */
> > > ret = advk_pcie_check_pio_status(pcie, allow_crs, val);
> > > if (ret < 0) {
> > > - *val = 0xffffffff;
> > > + SET_PCI_ERROR_RESPONSE(val);
> > > return PCIBIOS_SET_FAILED;
> > > }
> > >
> > > --
> > > 2.25.1
> > >
