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Date:   Fri, 22 Mar 2019 13:17:58 +0800
From:   Yifeng Li <>
To:     Sudip Mukherjee <>,
        Teddy Wang <>,
Cc:     Bartlomiej Zolnierkiewicz <>,,,
        Yifeng Li <>
Subject: [PATCH v2 6/7] fbdev: sm712fb: Kconfig: add information about docs.

This commits update the Kconfig description of sm712fb,
and inform the user about the existence of documentation.

Signed-off-by: Yifeng Li <>
 Documentation/fb/sm712fb.txt | 44 ++++++++++++++++++++----------------
 drivers/video/fbdev/Kconfig  |  4 ++++
 2 files changed, 29 insertions(+), 19 deletions(-)

diff --git a/Documentation/fb/sm712fb.txt b/Documentation/fb/sm712fb.txt
index 906b48aa40e4..c9a8fe059ac7 100644
--- a/Documentation/fb/sm712fb.txt
+++ b/Documentation/fb/sm712fb.txt
@@ -18,9 +18,10 @@ and it was also an inexpensive platform for non-x86 hobbyists to explore.
 How to use it?
-You should not compile-in vesafb, since SM7xx can be used in a VGA
-compatible mode, resulting conflicts with this driver. In addition,
-the VGA compatible mode was never tested by the maintainers.
+SM7xx can be used in a VGA compatible mode and a native framebuffer mode,
+this driver is a native driver. By default, it has no problem taking over
+the VGA driver automatically, but you should not attempt to use both at
+the same time.
 Currently, the driver supports 3 modes: 640x480, 800x600, 1024x768,
 at 16, 24 or 32-bit depth. Switching modes is done using the
@@ -44,30 +45,35 @@ alpha channel, it's otherwise equal to 24-bit color. However, they
 could still be useful. For example, "fbterm" supports 32-bit mode
 but not 24-bit mode.
-Notes about Modesetting
 The modesetting code in sm712fb has major problems.
-* Switching to 8-bit color mode will result in a black screen, so
-they are removed from the list of supported graphic modes. But they
-can still be switched to on-the-fly, don't do that then!
+* If you are using a laptop, using a non-native resolution (for example,
+using 640x480 on a 1024x768 screen) may garbled your LCD display, showing
+a white screen.
-* Only a refresh rate of 60 Hz is supported.
+* The driver assumes a 1024x768 LCD by default, if you have a rare 800x600,
+or 640x480 screen (e.g. Thinkpad 240X), it may garble your LCD by default.
+* The driver will crash/hang on systems with less than 2 MiB of VRAM,
+(e.g. Thinkpad 240X), it cannot be fixed because the maintainers don't
+have the hardware for testing.
-* 1024x768 with 16-bit color is not really supported, because the
-registers have been hacked by the original developer to adapt
-the 1024x600 screen on Lemote YeeLoong 8089.
+* Switching to 8-bit color mode will result in a black screen, so they are
+removed from the list of supported graphic modes. But they can still be
+switched to on-the-fly with fbset, don't do that then!
-* If you are using a Lemote YeeLoong 8089, please remember that only
-the 1024x768 modes are guaranteed to drive the LCD panel properly.
-Other modes are meant to drive a CRT, and may drive the LCD incorrectly
-and result in a white screen with random garbage. External VGA output is
+* It is not possible to use different resolutions for LCD and VGA out.
+* Only a refresh rate of 60 Hz is supported.
 Due to the way registers are hardcoded, it's impossible to fix them
-without a major code rewrite. If you've been hit by these problems badly
-and really need to get them fixed, please contact the driver maintainers.
+without a major code rewrite.
+If you've been hit by these problems badly and really need to get them
+fixed, please contact the driver maintainers.
 2D acceleration
@@ -97,7 +103,7 @@ Missing Features
 The following features are not implemented in this driver,
-	* 2D acceleration on SM720 and Big-Endian CPUs.
+	* 2D acceleration on Big-Endian CPUs.
 	* More VGA modes.
 	* dual-head support
 	* hardware cursor support
diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
index ae7712c9687a..4f3c0075352a 100644
--- a/drivers/video/fbdev/Kconfig
+++ b/drivers/video/fbdev/Kconfig
@@ -2302,6 +2302,10 @@ config FB_SM712
 	  called sm712fb. If you want to compile it as a module, say M
 	  here and read <file:Documentation/kbuild/modules.txt>.
+	  Warning: this driver has many known problems and limitations,
+	  please make sure you've checked the documentation, at
+	  <file:Documentation/fb/sm712fb.txt>.
 source "drivers/video/fbdev/omap/Kconfig"
 source "drivers/video/fbdev/omap2/Kconfig"
 source "drivers/video/fbdev/mmp/Kconfig"

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