linux-kernel - Re: [PATCH] PCI: Add cast when assigning PCI_ROM_ADDRESS

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Date:   Tue, 11 Apr 2017 19:28:46 +0200
From:   Mason <slash.tmp@...e.fr>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Grant Grundler <grundler@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Michael Davidson <md@...gle.com>
Subject: Re: [PATCH] PCI: Add cast when assigning PCI_ROM_ADDRESS_MASK to a
 32-bit variable

On 11/04/2017 19:23, Matthias Kaehlcke wrote:

> El Tue, Apr 11, 2017 at 12:08:38PM +0200 Mason ha dit:
> 
>> On 11/04/2017 03:24, Bjorn Helgaas wrote:
>>
>>> On Mon, Apr 10, 2017 at 03:24:57PM -0700, Matthias Kaehlcke wrote:
>>>
>>>> This fixes a clang warning about "implicit conversion from 'unsigned
>>>> long' to 'u32'"
>>>>
>>>> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
>>>> ---
>>>>  drivers/pci/probe.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>>>> index dfc9a2794141..148e80d5caf1 100644
>>>> --- a/drivers/pci/probe.c
>>>> +++ b/drivers/pci/probe.c
>>>> @@ -180,7 +180,7 @@ int __pci_read_base(struct pci_dev *dev, enum pci_bar_type type,
>>>>  	u16 orig_cmd;
>>>>  	struct pci_bus_region region, inverted_region;
>>>>  
>>>> -	mask = type ? PCI_ROM_ADDRESS_MASK : ~0;
>>>> +	mask = type ? (u32)PCI_ROM_ADDRESS_MASK : ~0;
>>>
>>> Can we put the cast in the PCI_ROM_ADDRESS_MASK #define so we don't have to
>>> repeat it in all the uses?
>>
>> Fixing these "implicit conversion" warnings, especially for
>> unsigned types, is a slippery slope. (The behavior of the
>> conversion is well-defined.)
>>
>> How about changing the type of PCI_ROM_ADDRESS_MASK instead?
>> It's defined as ~0x7ffUL but it's only used in the context
>> of u32.
>>
>> So make it an unsigned int:
>> #define PCI_ROM_ADDRESS_MASK (~0x7ffU)
>>
>> AFAIU, unsigned int is 32 bits on all platforms supported
>> by Linux.
> 
> I considered this initially, but wasn't sure if the unsigned long
> mask might be needed in some cases. From the comments I interpret that
> there should be no problems with using a 32 bit mask everywhere.
> 
> I'll send out an updated patch shortly.

Full disclaimer: I'm just a grunt with no knowledge of
the PCI framework. Bjorn is the authority here ;-)

Regards.