Re: [Qemu-devel] [PULL 2/3] ahci: Force ICC bits in PxCMD to zero

[John Snow]

On 07/21/2015 09:02 AM, Peter Maydell wrote:
> On 21 July 2015 at 13:55, Eric Blake <address@hidden> wrote:
>> On 07/21/2015 05:38 AM, Peter Maydell wrote:
>>> On 20 July 2015 at 19:29, John Snow <address@hidden> wrote:
>>>> From: Stefan Fritsch <address@hidden>
>>>>
>>>> The AHCI spec requires that the HBA sets the ICC bits to zero after the
>>>> ICC change is done. Since we don't do any ICC change, force the bits to
>>>> zero all the time.
>>>>
>>>> This fixes delays with some OSs (e.g. OpenBSD) waiting for the ICC bits
>>>> to change to 0.
>>>
>>> This change provokes a lot of clang sanitizer warnings:
>>>
>>> /home/petmay01/linaro/qemu-for-merges/hw/ide/ahci.c:288:49: runtime
>>> error: left shift of 15 by 28 places cannot be represented in type
>>> 'int'
>>>
>>> PORT_CMD_ICC_MASK is defined as
>>>
>>>  #define PORT_CMD_ICC_MASK         (0xf << 28) /* i/f ICC state mask */
>>>
>>> which shifts into the sign bit of a signed integer.
>>
>> Should be fixable by using (0xfU << 28), right?
> 
> Yes, though it assumes that if you say "~PORT_CMD_ICC_MASK"
> you're happy to only get a 32-bit mask. 0xfULL would avoid
> that (see discussion on the other thread with Paolo about
> the PPC similar issue.)
> 

I think we're happy to admit it's a simple 32bit mask, since it's just a
32bit field and I can't imagine us needing it for any other purpose
right now.

I'd be worried that ~(0xfULL) would be pretty much the wrong thing in
nearly all cases. Same for ~..UL.

I'll send a quick patch for Eric's suggestion.

> -- PMM
> 

Thanks,
--js