linux-kernel - Re: [PATCH 09/22] PCI: aardvark: Use SET_PCI_ERROR

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Date:   Mon, 11 Oct 2021 23:58:13 +0530
From:   Naveen Naidu <naveennaidu479@...il.com>
To:     Pali Rohár <pali@...nel.org>
Cc:     bhelgaas@...gle.com,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        "moderated list:PCI DRIVER FOR AARDVARK (Marvell Armada 3700)" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 09/22] PCI: aardvark: Use SET_PCI_ERROR_RESPONSE() when
 device not found

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@...il.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.

> >  		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
> >