linux-kernel - Re: [PATCH v3] NTB: switchtec_ntb: Update switchtec documentation with pre-requisites for NTB

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Message-ID: <20181011162747.GP5906@bhelgaas-glaptop.roam.corp.google.com>
Date:   Thu, 11 Oct 2018 11:27:47 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Wesley Sheng <wesley.sheng@...rochip.com>
Cc:     bhelgaas@...gle.com, corbet@....net, logang@...tatee.com,
        kurt.schwemmer@...rosemi.com, linux-ntb@...glegroups.com,
        linux-pci@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Wesley Yung <wesley.yung@...rochip.com>,
        Kelvin Cao <kelvin.cao@...rochip.com>,
        Jon Mason <jdmason@...zu.us>
Subject: Re: [PATCH v3] NTB: switchtec_ntb: Update switchtec documentation
 with pre-requisites for NTB

[+cc Jon Mason]

On Wed, Oct 10, 2018 at 10:42:55PM +0800, Wesley Sheng wrote:
> From: Wesley Yung <wesley.yung@...rochip.com>
> 
> The ntb_hw_switchtec driver has requirements on kernel configuration
> so we add these notes to the documentation and also clean up a few 
> other sentences in the documentation.
> 
> Signed-off-by: Wesley Yung <wesley.yung@...rochip.com>
> Signed-off-by: Kelvin Cao <kelvin.cao@...rochip.com>
> Signed-off-by: Wesley Sheng <wesley.sheng@...rochip.com>

I'm not sure who should really own this file:

  $ ./scripts/get_maintainer.pl -f Documentation/switchtec.txt
  Kurt Schwemmer <kurt.schwemmer@...rosemi.com> (maintainer:PCI DRIVER FOR MICROSEMI SWITCHTEC)
  Logan Gunthorpe <logang@...tatee.com> (maintainer:PCI DRIVER FOR MICROSEMI SWITCHTEC)
  Jonathan Corbet <corbet@....net> (maintainer:DOCUMENTATION)
  linux-pci@...r.kernel.org (open list:PCI DRIVER FOR MICROSEMI SWITCHTEC)
  linux-doc@...r.kernel.org (open list:DOCUMENTATION)
  linux-kernel@...r.kernel.org (open list)

and Jon (NTB driver core maintainer) has applied recent updates
to it.

But in the interest of forward progress, I applied this patch with
Logan's ack to pci/misc for v4.20.

> ---
>  Documentation/switchtec.txt | 30 ++++++++++++++++++++----------
>  1 file changed, 20 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/switchtec.txt b/Documentation/switchtec.txt
> index f788264..d6f04dcc 100644
> --- a/Documentation/switchtec.txt
> +++ b/Documentation/switchtec.txt
> @@ -23,7 +23,7 @@ The primary means of communicating with the Switchtec management firmware is
>  through the Memory-mapped Remote Procedure Call (MRPC) interface.
>  Commands are submitted to the interface with a 4-byte command
>  identifier and up to 1KB of command specific data. The firmware will
> -respond with a 4 bytes return code and up to 1KB of command specific
> +respond with a 4-byte return code and up to 1KB of command specific
>  data. The interface only processes a single command at a time.
>  
>  
> @@ -36,8 +36,8 @@ device: /dev/switchtec#, one for each management endpoint in the system.
>  The char device has the following semantics:
>  
>  * A write must consist of at least 4 bytes and no more than 1028 bytes.
> -  The first four bytes will be interpreted as the command to run and
> -  the remainder will be used as the input data. A write will send the
> +  The first 4 bytes will be interpreted as the Command ID and the
> +  remainder will be used as the input data. A write will send the
>    command to the firmware to begin processing.
>  
>  * Each write must be followed by exactly one read. Any double write will
> @@ -45,9 +45,9 @@ The char device has the following semantics:
>    produce an error.
>  
>  * A read will block until the firmware completes the command and return
> -  the four bytes of status plus up to 1024 bytes of output data. (The
> -  length will be specified by the size parameter of the read call --
> -  reading less than 4 bytes will produce an error.
> +  the 4-byte Command Return Value plus up to 1024 bytes of output
> +  data. (The length will be specified by the size parameter of the read
> +  call -- reading less than 4 bytes will produce an error.)
>  
>  * The poll call will also be supported for userspace applications that
>    need to do other things while waiting for the command to complete.
> @@ -83,10 +83,20 @@ The following IOCTLs are also supported by the device:
>  Non-Transparent Bridge (NTB) Driver
>  ===================================
>  
> -An NTB driver is provided for the switchtec hardware in switchtec_ntb.
> -Currently, it only supports switches configured with exactly 2
> -partitions. It also requires the following configuration settings:
> +An NTB hardware driver is provided for the Switchtec hardware in
> +ntb_hw_switchtec. Currently, it only supports switches configured with
> +exactly 2 NT partitions and zero or more non-NT partitions. It also requires
> +the following configuration settings:
>  
> -* Both partitions must be able to access each other's GAS spaces.
> +* Both NT partitions must be able to access each other's GAS spaces.
>    Thus, the bits in the GAS Access Vector under Management Settings
>    must be set to support this.
> +* Kernel configuration MUST include support for NTB (CONFIG_NTB needs
> +  to be set)
> +
> +NT EP BAR 2 will be dynamically configured as a Direct Window, and
> +the configuration file does not need to configure it explicitly.
> +
> +Please refer to Documentation/ntb.txt in Linux source tree for an overall
> +understanding of the Linux NTB stack. ntb_hw_switchtec works as an NTB
> +Hardware Driver in this stack.
> -- 
> 2.7.4
>