fbdev: Make BIOS EDID reading configurable

DDC reading via the Video BIOS may take several tens of seconds with some combination of display cards and monitors.

Make this option configurable and select only for drivers that need it.

---

 arch/i386/boot/video.S |    2 ++
 drivers/video/Kconfig  |   12 ++++++++++++
 drivers/video/fbmon.c  |    6 +++---
 3 files changed, 17 insertions(+), 3 deletions(-)

index 2ac40c8..0000a26 100644
@@ -1924,6 +1924,7 @@ skip10:	movb	%ah, %al
 	ret
 
 store_edid:
+#ifdef CONFIG_FB_FIRMWARE_EDID
 	pushw	%es				# just save all registers
 	pushw	%ax
 	pushw	%bx

@@ -1954,6 +1955,7 @@ store_edid:
 	popw	%bx
 	popw	%ax
 	popw	%es
+#endif
 	ret
 
 # VIDEO_SELECT-only variables

index e31390a..87384d3 100644
@@ -70,6 +70,18 @@ config FB_MACMODES
        depends on FB
        default n
 
+config FB_FIRMWARE_EDID
+       bool "Enable firmware EDID"
+       depends on FB
+       default n
+       ---help---
+         This enables access to the EDID transferred from the firmware.
+	 On the i386, this is from the Video BIOS. Enable this if DDC/I2C
+	 transfers do not work for your driver and if you are using
+	 nvidiafb, i810fb or savagefb.
+
+	 If unsure, say N.
+
 config FB_MODE_HELPERS
         bool "Enable Video Mode Handling Helpers"
         depends on FB

index 7c74e73..53beeb4 100644
@@ -1281,7 +1281,7 @@ int fb_validate_mode(const struct fb_var
 		-EINVAL : 0;
 }
 
-#if defined(__i386__)
+#if defined(CONFIG_FB_FIRMWARE_EDID) && defined(__i386__)
 #include <linux/pci.h>
 
 /*

@@ -1311,11 +1311,11 @@ const unsigned char *fb_firmware_edid(st
 {
 	return NULL;
 }
-#endif /* _i386_ */
+#endif
+EXPORT_SYMBOL(fb_firmware_edid);
 
 EXPORT_SYMBOL(fb_parse_edid);
 EXPORT_SYMBOL(fb_edid_to_monspecs);
-EXPORT_SYMBOL(fb_firmware_edid);
 EXPORT_SYMBOL(fb_get_mode);
 EXPORT_SYMBOL(fb_validate_mode);
 EXPORT_SYMBOL(fb_destroy_modedb);

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But that's not what the patch actually does - it requires that the user select the option.

Also, is it not possible to defer this operation until we've parsed the command line, control it with a kernel boot parameter?

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You got me there :-). Initially, I had:

select FB_FIRMWARE_EDID if ...

in Kconfig on selected drivers, but in the end removed it. And, I forgot to change the changelog.

The reason I removed the "select ..." part is because the user won't be able to deselect this option.

I thought of that, but it seems a bit complicated to me to parse boot options in assembly so I left this for another time.

The firmware EDID is only used as fallback, or if drivers have no DDC/I2C support. Currently, all drivers that use the firmware EDID also have I2C support in place. And chances are, if DDC transfers failed, the firmware EDID will also be absent.

Tony

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Well I'm wondering whether we can instead do this query later on, after we've entered start_kernel().

hm. Don't you think `default y' would be better? As it is, people's stuff will mysteriously stop working.

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The query is done while machine is in real mode (in arch/i386/boot/video.S).

Hmm. You're right, 'default y' looks better. Would you like me to send you a patch, or would you rather take care of it?

Tony

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Is OK, I'll diddle the diff.

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- Make CONFIG_FB_FIRMWARE_EDID default to yes
- Add more info to Kconfig help section on when to select N for this option

---

On second thought, I'll just send you an update.

Tony

 drivers/video/Kconfig |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

index e6a02d6..e9b5045 100644
@@ -73,14 +73,18 @@ config FB_MACMODES
 config FB_FIRMWARE_EDID
        bool "Enable firmware EDID"
        depends on FB
-       default n
+       default y
        ---help---
          This enables access to the EDID transferred from the firmware.
 	 On the i386, this is from the Video BIOS. Enable this if DDC/I2C
 	 transfers do not work for your driver and if you are using
 	 nvidiafb, i810fb or savagefb.
 
-	 If unsure, say N.
+	 In general, choosing Y for this option is safe.  If you 
+	 experience extremely long delays while booting before you get
+	 something on your display, try setting this to N.  Matrox cards in
+	 combination with certain motherboards and monitors are known to
+	 suffer from this problem.
 
 config FB_MODE_HELPERS
         bool "Enable Video Mode Handling Helpers"

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