Subject: Re: [PATCH v3 01/10] VAS: Define macros, register fields and structures

From: Sukadev Bhattiprolu <[email-masked]>
Date: Fri, 24 Mar 2017 14:30:09 -0700

Michael Neuling [[email-masked]] wrote:
> On Thu, 2017-03-16 at 20:33 -0700, Sukadev Bhattiprolu wrote:
> > Define macros for the VAS hardware registers and bit-fields as well
> > as couple of data structures needed by the VAS driver.
> > 
> > > Signed-off-by: Sukadev Bhattiprolu <[email-masked]>
> > ---
> > Changelog[v3]
> > 	- Rename winctx->pid to winctx->pidr to reflect that its a value
> > 	  from the PID register (SPRN_PID), not the linux process id.
> > 	- Make it easier to split header into kernel/user parts
> > 	- To keep user interface simple, use macros rather than enum for
> > 	  the threshold-control modes.
> > 	- Add a pid field to struct vas_window - needed for user space
> > 	  send windows.
> > 
> > Changelog[v2]
> > 	- Add an overview of VAS in vas-internal.h
> > 	- Get window context parameters from device tree and drop
> > 	  unnecessary macros.
> > ---
> >  MAINTAINERS                     |   6 +
> >  arch/powerpc/include/asm/vas.h  |  43 +++++
> >  drivers/misc/vas/vas-internal.h | 392 ++++++++++++++++++++++++++++++++++++++++
> 
> This is going to have to go through gregkh/lkml if it's drivers/misc.  you'll at
> least need gregkh's ack/ok before mpe will take them (which is what we did for
> CAPI).
> 
> We might want to keep this in arch/powerpc but I'm not sure.
> 

We will have device nodes accessible to user space so put it here and can
copy Gregkh next time. But let me know if we should move to arch/powerpc.

> >  3 files changed, 441 insertions(+)
> >  create mode 100644 arch/powerpc/include/asm/vas.h
> >  create mode 100644 drivers/misc/vas/vas-internal.h
> > 
> <snip>
> > +
> > +/*
> > + * Overview of Virtual Accelerator Switchboard (VAS).
> > + *
> > + * VAS is a hardware "switchboard" that allows senders and receivers to
> > + * exchange messages with _minimal_ kernel involvment. The receivers are
> > + * typically NX coprocessor engines that perform compression or encryption
> > + * in hardware, but receivers can also be other software threads.
> > + *
> > + * Senders are user/kernel threads that submit compression/encryption or
> > + * other requests to the receivers. Senders must format their messages as
> > + * Coprocessor Request Blocks (CRB)s and submit them using the instructions
> > + * "copy" and "paste" which were introduced in Power9.
> > + *
> > + * A Power node can have (upto?) 8 Power chips. There is one instance of
> > + * VAS in each Power9 chip. Each instance of VAS has 64K windows or ports,
> > + * Senders and receivers must each connect to a separate window before they
> > + * can exchange messages through the switchboard.
> > + *
> > + * Each window is described by two types of window contexts:
> > + *
> > > + *	Hypervisor Window Context (HVWC) of size VAS_HVWC_SIZE bytes
> > + *
> > > + *	OS/User Window Context (UWC) of size VAS_UWC_SIZE bytes.
> > + *
> > + * A window context can be viewed as a set of 64-bit registers. The settings
> > + * in these registers configure/control/determine the behavior of the VAS
> > + * hardware when messages are sent/received through the window. The registers
> > + * in the HVWC are configured by the kernel while the registers in the UWC can
> > + * be configured by the kernel or by the user space application that is using
> > + * the window.
> > + *
> > + * The HVWCs for all windows on a specific instance of VAS are in a contiguous
> > + * range of hardware addresses or Base address region (BAR) referred to as the
> > + * HVWC BAR for the instance. Similarly the UWCs for all windows on an instance
> > + * are referred to as the UWC BAR for the instance. The two BARs for each
> > + * instance are defined Power9 MMIO Ranges spreadsheet and available to the
> > + * kernel the device tree as follows:
> > + *
> > > + *	/proc/device-tree/xscom@.../vas@.../hvwc-bar-start
> > > + *	/proc/device-tree/xscom@.../vas@.../hvwc-bar-size
> > > + *	/proc/device-tree/xscom@.../vas@.../uwc-bar-start
> > + *	/proc/device-tree/xscom@.../vas@.../uwc-bar-size
> 
> should these just be reg properties?

I guess they could. Will try that
> 
> > + *
> > + * The kernel maps these two hardware address regions into the kernel address
> > + * space (hvwc_map and uwc_map) and accesses the window contexts of a specific
> > + * window using:
> > + *
> > > + *	 hvwc = hvwc_map + winid * VAS_HVWC_SIZE.
> > > + *	 uwc = uwc_map + winid * VAS_UWC_SIZE.
> > + *
> > + * where winid is the window index (0..64K).
> > + *
> > + * Note that the window contexts are used to "configure" the windows. In
> > + * addition to this configuration address, each _send_ window also has a
> > + * unique hardware address, referred to as the "paste-address" to which the
> > + * sender must "paste" the message (CRB) they wish to submit. This hardware
> > + * paste address for window can be computed from the following nodes in the
> > + * device tree:
> > + *
> > > + *	/proc/device-tree/xscom@.../vas@.../window-base
> > + *	/proc/device-tree/xscom@.../vas@.../window-shift
> 
> Same here with reg properties.

ok

> 
> <snip> 
> > +struct vas_winctx {
> <snip>
> > > +	int lpid;
> > +	int pidr;		/* value from SPRN_PID, not linux pid */
> 
> I'm surprised we have a copy of these here.  They should be accessed from the
> context we are attaching to, rather than copied here... but I've not looked at
> the rest of the code yet...

struct vas_winctx is just a convenient container for the window context.
It gets initialized based on type/use of window (user/kernel send/receive).
The lpid/pid are set by callers of VAS kernel interfaces.

Sukadev