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

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Message-ID: <17192051-ddd4-4cc8-a3a1-d8b2ac6a0b71@gmail.com>
Date: Thu, 16 Jan 2025 16:27:41 +0000
From: "Colin King (gmail)" <colin.i.king@...il.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.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 16/01/2025 16:18, Ilpo Järvinen wrote:
> 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.
> 

OK, I'll send a patch later today.

Colin

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