[Skiboot] [RFC 0/3] phb4/capp: Provide user tunable for STQ/DMA engine allocation

Vaibhav Jain vaibhav at linux.ibm.com
Mon Sep 10 19:01:01 AEST 2018

Andrew Donnellan <andrew.donnellan at au1.ibm.com> writes:

> On 10/09/18 15:23, Vaibhav Jain wrote:
>> Thanks for looking into these patches Andrew,
>> Andrew Donnellan <andrew.donnellan at au1.ibm.com> writes:
>>> While NVRAM attributes might be a good idea for bringup/enablement
>>> environments I think it's not ideal for doing device-specific
>>> configuration in production environments.
>> This is more likely AFU specific rather than device specific. Since the
>> split between coherent/dma traffic might be specific to an AFU hence its
>> difficult to comeup with an optimal default.
> Right, when I say "device-specific" I'm really getting at "AFU 
> specific", obviously for FPGA cards it's about the AFU not about the 
> FPGA model.
Ok thanks for clarifying this.

> By extension, if skiboot exposed this to Linux, Linux can in turn expose 
> it via the driver or via the internal kernel API so that AFU-specific 
> code can set it.
Agree, and this a similar model used for CX5 adapter init. However not
many AFU designers (atleast in case of CAPI2) will be writing there own
drivers and will rely on CXL module to interact with their cards. So it
would be better to expose this via CXL or some sysfs attribute to the
PCI bridge. This would also need a new opal call to init capp so that
can be send these values down to skiboot's capp init code.

The values are populated during the CAPP init that happens in middle of
the card probe. So their values are needed very early during the init
phase. Resetting them would need a re-init of CAPP.

> -- 
> Andrew Donnellan              OzLabs, ADL Canberra
> andrew.donnellan at au1.ibm.com  IBM Australia Limited

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

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