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Date: Fri, 12 Feb 2010 15:05:55 -0800
From: Randy Dunlap <rdunlap@...otime.net>
To: Jason Wessel <jason.wessel@...driver.com>
CC: linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
mingo@...e.hu
Subject: Re: [PATCH 6/7] kgdb,docs: Update the kgdb docs to include kms
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@...driver.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=<serial_device>[,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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