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

From: Michael Neuling <[email-masked]>
Date: Fri, 24 Mar 2017 15:22:20 +1100

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.

>  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?

> + *
> + * 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.

<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...