[PATCH 5/5] powerpc/fsl_msi: add 'msiregs' kernel parameter

[Scott Wood]

On 06/17/2013 12:36:50 AM, Lian Minghuan-b31939 wrote:
> Hi Scott,
> 
> please see my comments inline.
> 
> On 06/15/2013 06:13 AM, Scott Wood wrote:
>> On 06/14/2013 02:15:59 AM, Minghuan Lian wrote:
>>> 1. Only MSIIR1 can index 16 MSI registers, but when using MSIIR1
>>> the IRQs of a register are not continuous. for example, the first
>>> register irq values are 0x0, 0x10, 0x20, 0x30 ... 0x1f0. So it
>>> is hard to use 'msi-available-ranges' property to indicate the
>>> available ranges and 'msi-available-ranges' property has been
>>> removed from dts node, so this patch removes the related code.
>>> 
>>> 2. Add 'msiregs' kernel parameter instead of 'msi-available-ranges'
>>> functionality.
>> 
>> The reason we used a device tree property was because this is for  
>> virtualization and AMP scenarios where this instance of Linux does  
>> not own all of the MSI registers.
>> 
>> I don't see any reasonable way to partition an MPIC v4.3 MSI group  
>> -- but there are more groups, so it's not that bad.  What's the use  
>> case for this patch?
>> 
> [Minghuan] I do not known any case about this patch. I add 'msiregs'  
> just for achieving "msi-available-ranges" functionality. I do not  
> want to remove partition functionality when updating to mpic4.3,  
> although I do not see virtualization and AMP cases on T4(KVM does not  
> need this functionality).

Such functionality does not work on mpic v4.3.  There are conflicting  
requirements of contiguous MSIs (because PCI devices can use them that  
way) and the inability to partition a single register (because they all  
go to the same MPIC interrupt).

Keep msi-available-ranges as is for older hardware, and just ignore it  
(with a warning printed) if it's present on MPIC v4.3.

-Scott