From: "Pali Rohár" <pali@kernel.org>
To: Naveen Naidu <naveennaidu479@gmail.com>
Cc: bhelgaas@google.com,
linux-kernel-mentees@lists.linuxfoundation.org,
linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
"Rob Herring" <robh@kernel.org>,
"Krzysztof Wilczyński" <kw@linux.com>,
"moderated list:PCI DRIVER FOR AARDVARK (Marvell Armada 3700)"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 09/22] PCI: aardvark: Use SET_PCI_ERROR_RESPONSE() when device not found
Date: Mon, 11 Oct 2021 20:41:44 +0200 [thread overview]
Message-ID: <20211011184144.qcbmif7hvzozdgzw@pali> (raw)
In-Reply-To: <20211011182526.kboaxqofdpd2jjrl@theprophet>
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@gmail.com>
> > > ---
> > > 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@gmail.com/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
> > >
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next prev parent reply other threads:[~2021-10-11 18:44 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-11 17:35 [PATCH 00/22] PCI: Unify PCI error response checking Naveen Naidu
2021-10-11 17:37 ` [PATCH 01/22] PCI: Add PCI_ERROR_RESPONSE and it's related defintions Naveen Naidu
2021-10-11 17:45 ` [PATCH 03/22] PCI: thunder: Use SET_PCI_ERROR_RESPONSE() when device not found Naveen Naidu
2021-10-11 17:46 ` [PATCH 04/22] PCI: iproc: " Naveen Naidu
2021-10-11 17:51 ` [PATCH 05/22] PCI: mediatek: " Naveen Naidu
2021-10-11 17:52 ` [PATCH 06/22] PCI: exynos: " Naveen Naidu
2021-10-11 17:56 ` [PATCH 09/22] PCI: aardvark: " Naveen Naidu
2021-10-11 18:08 ` Pali Rohár
2021-10-11 18:28 ` Naveen Naidu
[not found] ` <20211011182526.kboaxqofdpd2jjrl@theprophet>
2021-10-11 18:41 ` Pali Rohár [this message]
2021-10-12 15:59 ` Naveen Naidu
2021-10-13 2:13 ` Bjorn Helgaas
2021-10-13 17:59 ` Pali Rohár
2021-10-11 18:00 ` [PATCH 10/22] PCI: mvebu: " Naveen Naidu
2021-10-11 18:02 ` [PATCH 13/22] PCI: rockchip: " Naveen Naidu
2021-10-11 18:13 ` [PATCH 22/22] PCI: xgene: Use PCI_ERROR_RESPONSE to specify hardware error Naveen Naidu
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