On 2012-10-22 20:43, Greg Kroah-Hartman wrote:
On Mon, Oct 22, 2012 at 11:21:16AM -0500, H Hartley Sweeten wrote:
On Saturday, October 20, 2012 11:37 AM, Ian Abbott wrote:
On 20/10/12 04:44, Dan Carpenter wrote:
On Mon, Oct 15, 2012 at 01:07:33PM +0100, Ian Abbott wrote:
Change the type of the context parameter passed to
`comedi_auto_config_helper()` from `void *` to `unsigned long`. It's
currently just an internal change and all current internal usages pass
pointers in the context, but future uses of this function may pass
^^^
integer values
"May?" Don't make this kind of change until you have a user ready.
Using an unsigned long is uglier than using a void pointer so let's
not do it until it is needed.
Obviously the same thing would apply to the other places.
Patch 6 passes an unsigned integer value in the context. In the end,
the context probably won't be used much, but it's handy to have it in
case it's needed.
Patch 6 has a different issue..
You want to change the context from a void * to an unsigned long.. OK..
In Patch 6 you are passing a context of COMEDI_AUTO_ATTACH_{PCI,USB}.
You define these as:
+/* auto_attach() context values */
+#define COMEDI_AUTO_ATTACH_PCI (-1UL) /* from comedi_pci_auto_config() */
+#define COMEDI_AUTO_ATTACH_USB (-2UL) /* from comedi_usb_auto_config() */
Seems goofy... -1 and -2 are not 'unsigned'...
To me it just seems cleaner to leave the context as a void *. If you want
to pass a non-pointer context, cast that context to a void * and then back
to its real type when used. Casting a context that is a pointer to some type
of struct to an unsigned long and then back to the struct seems messy.
Just my opinion...
I agree with this, and I'll take it even farther, why do we need a
context variable at all? Shouldn't we be able to live with a properly
defined type here? We have control over the code, can't it be cleaned
up to use an enum or something, that would define the above values
properly?
Say if a single comedi driver handled both PCMCIA and PCI devices. It's
single auto_attach() routine would need some way to tell what sort of
device it is dealing with (not that auto-attachment of PCMCIA devices is
currently supported, but it should be easy enough to do).
If a driver needed to allocate some memory before calling
comedi_auto_config() and pass the memory through to its auto_attach()
routine, the context parameter could be used for this purpose.
Relying on a context value to be a "magic" one is ripe for errors and
confusion.
Most drivers would just ignore the context value anyway, but the "magic"
values would only matter if they used a predefined wrapper around
comedi_auto_config(), such as comedi_pci_auto_config(). The same driver
shouldn't really mix direct calls of comedi_auto_config() with the calls
to the predefined wrappers such as comedi_pci_auto_config() as that
could lead to errors and confusion, although I tried to reduce this
possibility by representing the magic values in a similar way to
ERR_PTR() values.
--
-=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@xxxxxxxxx> )=-
-=( Tel: +44 (0)161 477 1898 FAX: +44 (0)161 718 3587 )=-
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