[GitHub] [incubator-nuttx] xiaoxiang781216 commented on a change in pull request #151: Fix kconfig warning

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xiaoxiang781216 commented on a change in pull request #151: Fix kconfig warning
URL: https://github.com/apache/incubator-nuttx/pull/151#discussion_r370443637
 
 

 ##########
 File path: arch/arm/src/lpc31xx/Kconfig
 ##########
 @@ -60,7 +60,7 @@ config LPC31_SPI
 config LPC31_USBOTG
 	bool "USB OTG"
 	default n
-	select USBHOST_HAVE_ASYNCH
+	select USBHOST_HAVE_ASYNCH if USBHOST
 
 Review comment:
   Yes, I follow STM32. But actually, I think there are many places which misuse select/depend/if.
   I copy the related stuff from https://www.kernel.org/doc/Documentation/kbuild/kconfig-language.txt:
   - reverse dependencies: "select" <symbol> ["if" <expr>]
     While normal dependencies reduce the upper limit of a symbol (see
     below), reverse dependencies can be used to force a lower limit of
     another symbol. The value of the current menu symbol is used as the
     minimal value <symbol> can be set to. If <symbol> is selected multiple
     times, the limit is set to the largest selection.
     Reverse dependencies can only be used with boolean or tristate
     symbols.
     Note:
   	select should be used with care. select will force
   	a symbol to a value without visiting the dependencies.
   	By abusing select you are able to select a symbol FOO even
   	if FOO depends on BAR that is not set.
   	In general use select only for non-visible symbols
   	(no prompts anywhere) and for symbols with no dependencies.
   	That will limit the usefulness but on the other hand avoid
   	the illegal configurations all over.
   
   - weak reverse dependencies: "imply" <symbol> ["if" <expr>]
     This is similar to "select" as it enforces a lower limit on another
     symbol except that the "implied" symbol's value may still be set to n
     from a direct dependency or with a visible prompt.
   This document has many bad example.
   

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