linux-kernel - re: PCI: Add TLP Prefix reading to pcie_read_tlp

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Message-ID: <de2a07a1-ea99-20d7-69c5-8fdf2f432750@linux.intel.com>
Date: Thu, 16 Jan 2025 18:18:47 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: "Colin King (gmail)" <colin.i.king@...il.com>, 
    Krzysztof Wilczyński <kw@...ux.com>, 
    Bjorn Helgaas <bhelgaas@...gle.com>
cc: Mahesh J Salgaonkar <mahesh@...ux.ibm.com>, 
    Oliver O'Halloran <oohall@...il.com>, 
    Jonathan Cameron <Jonathan.Cameron@...wei.com>, linux-pci@...r.kernel.org, 
    "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: re: PCI: Add TLP Prefix reading to pcie_read_tlp_log()

On Thu, 16 Jan 2025, Colin King (gmail) wrote:

> Hi,
> 
> Static analysis shows there is a potential issue in the following commit:
> 
> commit 00048c2d5f113bb4e82a0a30dfc4ee12590b81f5
> Author: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> Date:   Tue Jan 14 19:08:39 2025 +0200
> 
>     PCI: Add TLP Prefix reading to pcie_read_tlp_log()
> 
> 
> The issue is described as follows:
> 
> unsigned int aer_tlp_log_len(struct pci_dev *dev, u32 aercc)
> {
>         return PCIE_STD_NUM_TLP_HEADERLOG +
>                (aercc & PCI_ERR_CAP_PREFIX_LOG_PRESENT) ?
>                dev->eetlp_prefix_max : 0;
> }
> 
> 
> static analysis is warning that the left hand size of the ? operator is always
> true and so dev->eetlp_prefix_max is always being returned and the 0 is never
> returned (dead code).
> 
> I suspect the expected behaviour is as follows:
> 
>         return PCIE_STD_NUM_TLP_HEADERLOG +
>                ((aercc & PCI_ERR_CAP_PREFIX_LOG_PRESENT) ?
>                dev->eetlp_prefix_max : 0);
> 
> ..I'm reluctant to send a fix in case this is not the original intention.

Your fix looks correct, it should have the parenthesis due to operator 
precedence rules. The intention is to calculate 4 DWs + optionally n E-E 
TLP prefixes.

-- 
 i.