[Skiboot] [PATCH] phb4, doc: Make GPU-Direct bandwidth optimizations Witherspoon specific

[Vaibhav Jain]

Thanks for reviewing the patch Andrew

Andrew Donnellan <andrew.donnellan at au1.ibm.com> writes:
> On 28/07/18 18:17, Vaibhav Jain wrote:
>> Patch 5690c5a8980f("phb4: Reallocate PEC2 DMA-Read engines to improve
>> GPU-Direct bandwidth") introduced allocation of extra DMA-read engines
>> for improving Mellanox CX5 GPU-Direct bandwidth. At present CX5 is the
>> only card thats using these optimizations so these changes will only
>> impact Witherspoon systems.
>> 
>> However hardware team has raised the possibility of other
>> non-witherspoon systems in future that may be using a similar card,
>> where these optimizations wont be needed. So they have asked us to
>> make these changes Witherspoon specific.
>> 
>> Hence this patch updates the phb4_init_capp_regs() &
>> enable_capi_mode() to configure the extra DMA-read engine allocation
>> if and only if skiboot is running on Witherspoon platform.
>> 
>> Cc: stable #5.0.6+
>
> I suspect you mean 6.0.6 :)
Yes. Thanks for catching this. I will resent the patch.

>
> Hmm, a bit ugly, it'll be the only place in skiboot where we do anything 
> based on platform name. Though the other option that comes to mind is 
> adding an extra flag to struct platform, idk if this is big enough to 
> warrant that.
I agree. But AFAIK this is the only Witherspoon specific change right
now. If begin to have more of them then we probably will have to look
into CAPP specific quirks


-- 
Vaibhav Jain <vaibhav at linux.vnet.ibm.com>
Linux Technology Center, IBM India Pvt. Ltd.