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

Vaibhav Jain vaibhav at linux.ibm.com
Wed Aug 1 16:07:11 AEST 2018

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.

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