On Thu, Jan 03, 2013 at 10:14:13AM +0100, Julia Lawall wrote: > On Thu, 3 Jan 2013, Dan Carpenter wrote: > > > On Wed, Jan 02, 2013 at 06:31:53PM +1300, Tony Prisk wrote: > > > On Wed, 2013-01-02 at 08:10 +0300, Dan Carpenter wrote: > > > > clk_get() returns NULL if CONFIG_HAVE_CLK is disabled. > > > > > > > > I told Tony about this but everyone has been gone with end of year > > > > holidays so it hasn't been addressed. > > > > > > > > Tony, please fix it so people don't apply these patches until > > > > clk_get() is updated to not return NULL. It sucks to have to revert > > > > patches. > > > > > > > > regards, > > > > dan carpenter > > > > > > I posted the query to Mike Turquette, linux-kernel and linux-arm-kernel > > > mailing lists, regarding the return of NULL when HAVE_CLK is undefined. > > > > > > Short Answer: A return value of NULL is valid and not an error therefore > > > we should be using IS_ERR, not IS_ERR_OR_NULL on clk_get results. > > > > > > I see the obvious problem this creates, and asked this question: > > > > > > If the driver can't operate with a NULL clk, it should use a > > > IS_ERR_OR_NULL test to test for failure, rather than IS_ERR. > > > > > > > > > And Russell's answer: > > > > > > Why should a _consumer_ of a clock care? It is _very_ important that > > > people get this idea - to a consumer, the struct clk is just an opaque > > > cookie. The fact that it appears to be a pointer does _not_ mean that > > > the driver can do any kind of dereferencing on that pointer - it should > > > never do so. > > > > > > Thread can be viewed here: > > > https://lkml.org/lkml/2012/12/20/105 > > > > > > > Ah. Grand. Thanks... > > > > Btw. The documentation for clk_get() really should include some of > > this information. I know Russell thinks that the driver authors are > > stupid and lazy, and it's probably true. But if everyone makes the > > same mistake over and over, then it probably means we could put a > > special note: > > > > "Do not check this with IS_ERR_OR_NULL(). Null values are not an > > error. Drivers should treat the return value as an opaque cookie > > and they should not dereference it." > > > > This is probably there in the file somewhere else, but I searched > > for "opaque", "cookie", and "dereference" and I didn't find > > anything. I'm not saying the documentation isn't perfect, just that > > driver authors are lazy and stupid but we can't kill them so we have > > to live with them. > > I still think it would also be helpful for the definition that returns > NULL to have some documentation associated with it. Having a feature > disabled and then trying to use the feature could reasonably considered to > lead to a failure, so it is not obvious what the NULL represents. /** * clk_get - lookup and obtain a reference to a clock producer. * @dev: device for clock "consumer" * @id: clock consumer ID * * Returns a struct clk corresponding to the clock producer, or * valid IS_ERR() condition containing errno. The implementation * uses @dev and @id to determine the clock consumer, and thereby * the clock producer. (IOW, @id may be identical strings, but * clk_get may return different clock producers depending on @dev.) * * Drivers must assume that the clock source is not enabled. * * clk_get should not be called from within interrupt context. */ -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
