RE: [PATCH] staging/comedi: fix sparse warning: shift too big

[Hartley Sweeten]

On Friday, May 02, 2014 9:50 AM, Ian Abbott wrote:
> On 2014-05-02 15:57, Brilliantov Kirill Vladimirovich wrote:
>> Signed-off-by: Brilliantov Kirill Vladimirovich <brilliantov@xxxxxxxx>
>> ---
>>   drivers/staging/comedi/drivers/ni_stc.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/staging/comedi/drivers/ni_stc.h b/drivers/staging/comedi/drivers/ni_stc.h
>> index f0630b78..197b568 100644
>> --- a/drivers/staging/comedi/drivers/ni_stc.h
>> +++ b/drivers/staging/comedi/drivers/ni_stc.h
>> @@ -717,7 +717,7 @@ enum AI_AO_Select_Bits {
>>   static inline unsigned ni_stc_dma_channel_select_bitfield(unsigned channel)
>>   {
>>   	if (channel < 4)
>> -		return 1 << channel;
>> +		return 1 << (channel & 0x3);
>>   	if (channel == 4)
>>   		return 0x3;
>>   	if (channel == 5)
>>
>
> The warning seems a bit spurious!

The whole mite.c driver and it's users are all a bit of a mess.

I did find the information about the "AI AO Select Register" in the National
Instruments PCI E Series manual:

-----

The AI AO Select Register contains 8 bits that control the logical DMA selection for the
analog input and analog output resources. The contents of this register are cleared upon power
up and after a reset condition.
	Address:	base address + 0x09
	Type:		write-only
	Word size:	8-bit

	Bit	Name		Description
	7-4	Reserved	Reserved-Always write 0 to these bits (for PCI-6032E
				and PCI-6033E only).
	7-4	Output<D..A>	Analog Output Logical Channel D through A-These four
				bits select the logical channels of the MITE to be used by
				the analog output. You can only set one of these bits at a
				time (except for the PCI-6032E and PCI-6033E).
	3-0	Input<D..A>	Analog Input Logical Channel D through A-These four
				bits select the logical channels to be used by the analog
				input. You can only set one of these bits at a time.

-----

Based on this the ni_stc_dma_channel_select_bitfield() function appears to be
incorrect. The "channel"s should only be in the range 0 to 3 and result in a returned
bitfield of:

	channel	bitfield	Description
	0		0x01	Analog Input or Output Channel A
	1		0x02 	Analog Input or Output Channel B
	2		0x04 	Analog Input or Output Channel C
	3		0x08 	Analog Input or Output Channel D

Just my two cents...

Hartley

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