Hi Tomi,

On 02/29/2012 10:21 AM, Tomi Valkeinen wrote:

On Wed, 2012-02-29 at 10:03 +0000, Florian Tobias Schandinat wrote:

quoted

On 02/29/2012 08:48 AM, Tomi Valkeinen wrote:

quoted

panel-dvi uses i2c, but the Kconfig didn't have dependency on I2C. Add
it.

Signed-off-by: Tomi Valkeinen <redacted>
---
 drivers/video/omap2/displays/Kconfig |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/video/omap2/displays/Kconfig b/drivers/video/omap2/displays/Kconfig
index 74d29b5..408a992 100644
--- a/drivers/video/omap2/displays/Kconfig
+++ b/drivers/video/omap2/displays/Kconfig

@@ -12,7 +12,7 @@ config PANEL_GENERIC_DPI
 
 config PANEL_DVI
 	tristate "DVI output"
-	depends on OMAP2_DSS_DPI
+	depends on OMAP2_DSS_DPI && I2C

It's just a matter of taste, but are you sure you want to "depend" on it and not
"select" it? Other drivers tend to use select for I2C, for me it doesn't really
matter.

Well, I'd like to "select", but I don't think that's correct. From
Documentation/kbuild/kconfig-language.txt:

        In general use select only for non-visible symbols
        (no prompts anywhere) and for symbols with no dependencies.

But I do see quite many selects for I2C, so I'm not sure if all those
are wrong, or has it just been decided that I2C is a valid target for
select.

I'd say that the above is only a guideline but not absolute rule. For I2C I'd
argue that I probably wouldn't even know that my hardware has it if I weren't
the one writing the driver using it.
But it's true that select should be used with care as it is much easier to get
the config messed up by using it.

Using depend is in line with the other panel drivers in the same
directory. I've been thinking about the same thing from time to time,
and I'd rather select I2C, SPI and BACKLIGHT_CLASS_DEVICE than use
depend.

But, for example, using select to BACKLIGHT_CLASS_DEVICE is broken: if I
change a panel driver to select BACKLIGHT_CLASS_DEVICE, but then I
manually disable CONFIG_BACKLIGHT_LCD_SUPPORT (which the
BACKLIGHT_CLASS_DEVICE depends on) from the kernel config, this leads to
BACKLIGHT_CLASS_DEVICE being enabled, but CONFIG_BACKLIGHT_LCD_SUPPORT
being disabled, which is clearly broken.

Yes, as far as I understand the problem here is that we don't have any mechanism
to handle transitive dependencies (probably because we don't want it). So if one
wants to do select something I think the right way to do it would be to inherit
all its select/depend statements in the option.

So... As I see it, depending is a bit awkward, but it's correct.

Yes, it certainly is correct.


Best regards,

Florian Tobias Schandinat