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Date: Fri, 12 Feb 2010 15:05:55 -0800
From: Randy Dunlap <rdunlap@xenotime.net>
Organization: YPO4
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To: Jason Wessel <jason.wessel@windriver.com>
CC: linux-kernel@vger.kernel.org, kgdb-bugreport@lists.sourceforge.net,
       mingo@elte.hu
Subject: Re: [PATCH 6/7] kgdb,docs: Update the kgdb docs to include kms
References: <1266014188-29505-1-git-send-email-jason.wessel@windriver.com> <1266014188-29505-7-git-send-email-jason.wessel@windriver.com>
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On 02/12/10 14:36, Jason Wessel wrote:
> Update the kgdb docs to include information about kernel mode setting support.
> 
> Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
> ---
>  Documentation/DocBook/kgdb.tmpl     |   82 +++++++++++++++++++++++++++++++----
>  Documentation/kernel-parameters.txt |    9 +++-
>  2 files changed, 79 insertions(+), 12 deletions(-)
> 
> diff --git a/Documentation/DocBook/kgdb.tmpl b/Documentation/DocBook/kgdb.tmpl
> index cc81879..498267b 100644
> --- a/Documentation/DocBook/kgdb.tmpl
> +++ b/Documentation/DocBook/kgdb.tmpl
> @@ -200,12 +200,29 @@
>     only make use of <constant>kgdbwait</constant> and early debugging
>     if you build kgdboc into the kernel as a builtins.
>     </para>
> +   <para>Optionally you can elect to activate kms (Kernel Mode
> +   Setting) integration.  When you use kms with kgdboc and you have a
> +   video driver that has atomic mode setting hooks, it is possible to
> +   enter the debugger on the graphics console.  When the kernel
> +   execution is resumed, the graphics previous graphics mode will get

                   drop first  "graphics" above ...        mode will be

> +   restored.  This integration can serve as a useful tool to aid in
> +   dianosing crashes or doing analysis of memory with kdb while

      diagnosing

> +   allowing the full graphics console applications to run.
> +   </para>
>     <sect2 id="kgdbocArgs">
>     <title>kgdboc arguments</title>
> -   <para>Usage: <constant>kgdboc=[kbd][[,]serial_device][,baud]</constant></para>
> -   <para>You can configure kgdboc to use the keyboard, and or a serial device
> -   depending on if you are using kdb and or kgdb, in one of the
> -   following scenarios.
> +   <para>Usage: <constant>kgdboc=[kms][[,]kbd][[,]serial_device][,baud]</constant></para>
> +   <para>Abreviations:
> +   <itemizedlist>
> +   <listitem><para>kms = Kernel Mode Setting</para></listitem>
> +   <listitem><para>kbd = Keyboard</para></listitem>
> +   </itemizedlist>
> +   </para>
> +   <para>You can configure kgdboc to use the keyboard, and or a serial
> +   device depending on if you are using kdb and or kgdb, in one of the
> +   following scenarios.  The order listed above must be observed if
> +   you use any of the optional configurations together.  Using kms +
> +   only gdb is generally not a usful combination.

                                  useful

>     <orderedlist>
>     <listitem><para>kdb and kgdb over only a serial port</para>
>     <para><constant>kgdboc=&lt;serial_device&gt;[,baud]</constant></para>
> @@ -218,6 +235,12 @@
>     <listitem><para>kdb with a keyboard</para>
>     <para><constant>kgdboc=kbd</constant></para>
>     </listitem>
> +   <listitem><para>kdb with kernel modesetting</para>
> +   <para><constant>kgdboc=kms,kbd</constant></para>
> +   </listitem>
> +   <listitem><para>kdb with kernel modesetting and kgdb over a serial port</para>
> +   <para><constant>kgdboc=kbd,kbd,ttyS0,115200</constant></para>
> +   </listitem>
>     </orderedlist>
>     </para>
>     <para>You can configure kgdboc via sysfs or a module or kernel boot line
> @@ -613,6 +636,8 @@ Task Addr       Pid   Parent [*] cpu State Thread     Command
>        <listitem><para>The logic to perform safe memory reads and writes to memory while using the debugger</para></listitem>
>        <listitem><para>A full implementation for software breakpoints unless overridden by the arch</para></listitem>
>        <listitem><para>The API to invoke either the kdb or kgdb frontend to the debug core.</para></listitem>
> +      <listitem><para>The structures and call back API for atomic kernel mode setting.</para>

                                            callback

> +      <para>NOTE: kgdboc is where the kms callbacks are invoked.</para></listitem>
>        </itemizedlist>
>        </para>
>        </listitem>
> @@ -721,6 +746,8 @@ Task Addr       Pid   Parent [*] cpu State Thread     Command
>    </sect1>
>    <sect1 id="kgdbocDesign">
>    <title>kgdboc internals</title>
> +  <sect2>
> +  <title>kgdboc and uarts</title>
>    <para>
>    The kgdboc driver is actually a very thin driver that relies on the
>    underlying low level to the hardware driver having "polling hooks"
> @@ -729,10 +756,7 @@ Task Addr       Pid   Parent [*] cpu State Thread     Command
>    low level uart hook for doing polled mode reading and writing of a

     I prefer UART, but, oh well.

>    single character while in an atomic context.  When kgdb makes an I/O
>    request to the debugger, kgdboc invokes a call back in the serial
> -  core which in turn uses the call back in the uart driver.  It is

                                 callback in the UART

> -  certainly possible to extend kgdboc to work with non-uart based

                                                      non-UART-based

> -  consoles in the future.
> -  </para>
> +  core which in turn uses the call back in the uart driver.</para>

                                 callback

>    <para>
>    When using kgdboc with a uart, the uart driver must implement two callbacks in the <constant>struct uart_ops</constant>. Example from drivers/8250.c:<programlisting>
>  #ifdef CONFIG_CONSOLE_POLL
> @@ -746,9 +770,49 @@ Task Addr       Pid   Parent [*] cpu State Thread     Command
>    that they can be called from an atomic context and have to restore
>    the state of the uart chip on return such that the system can return
>    to normal when the debugger detaches.  You need to be very careful
> -  with any kind of lock you consider, because failing here is most
> +  with any kind of lock you consider, because failing here is most likely
>    going to mean pressing the reset button.
>    </para>
> +  </sect2>
> +  <sect2 id="kgdbocKbd">
> +  <title>kgdboc and keyboards</title>
> +  <para>The kgdboc driver contains logic to configure communications
> +  with an attached keyboard.  The keyboard infrastructure is only
> +  compiled into the kernel when CONFIG_KDB_KEYBOARD=y is set in the
> +  kernel configuration.</para>
> +  <para>The core polled keyboard driver driver for PS/2 type keyboards
> +  is in drivers/char/kdb_keyboard.c.  This driver is hooked into the
> +  debug core when kgdboc populates the callback in the arrary

                                                          array

> +  called <constant>kdb_poll_funcs[]</constant>.  The
> +  kdb_get_kbd_char() is the top level function which polls hardware

                               top-level

> +  for single character input.
> +  </para>
> +  </sect2>
> +  <sect2 id="kgdbocKms">
> +  <title>kgdboc and kms</title>
> +  <para>The kgdboc driver contains logic to request the grpahics

                                                           graphics

> +  display to switch to a text context if you are using
> +  kgdboc=kms,... and you have a video driver which has a framebuffer
> +  console and atomic kernel mode setting support.  Every time kernel
> +  debugger is entered it calls kgdboc_pre_exp_handler() which in turn
> +  calls dbg_kms_ops->activate_console().  On resuming kernel
> +  execution, the kernel debugger calls kgdboc_post_exp_handler() which
> +  in turn calls dbg_kms_ops->restore_console().</para>
> +  <para>Any video driver that wants to be compatible with the kernel
> +  debugger and the atomic kms callbacks must implement the
> +  mode_set_base_atomic operation.  The following is an example from
> +  drivers/gpu/drm/i915/intel_display.c:
> +  <informalexample>
> +  <programlisting>
> +static const struct drm_crtc_helper_funcs intel_helper_funcs = {
> +[...]
> +        .mode_set_base_atomic = intel_pipe_set_base_atomic,
> +[...]
> +};
> +  </programlisting>
> +  </informalexample>
> +  </para>
> +  </sect2>
>    </sect1>
>    </chapter>
>    <chapter id="credits">
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index af8b8e8..b340445 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1106,9 +1106,12 @@ and is between 256 and 4096 characters. It is defined in the file
>  	kgdboc=		[KGDB,HW] kgdb over consoles.
>  			Requires a tty driver that supports console polling,
>  			or a supported polling keyboard driver (non-usb).
> -			Serial only format: <serial_device>[,baud]
> -			keyboard only format: kbd
> -			keyboard and serial format: kbd,<serial_device>[,baud]
> +			 Serial only format: <serial_device>[,baud]
> +			 keyboard only format: kbd
> +			 keyboard and serial format: kbd,<serial_device>[,baud]
> +			Optional Kernal mode setting:

                                 Kernel

> +			 kms, kbd format: kms,kbd
> +			 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
>  
>  	kgdbwait	[KGDB] Stop kernel execution and enter the
>  			kernel debugger at the earliest opportunity if


-- 
~Randy
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