Re: [PATCH stable 3.9 to 3.16] staging: comedi: quatech_daqp_cs: fix no-op loop daqp_ao_insn_write()

[Ian Abbott <abbotti@mev.co.uk>]

On 09/11/18 23:44, Ben Hutchings wrote:
> On Tue, 2018-07-10 at 18:02 +0100, Ian Abbott wrote:
>> From: Dan Carpenter <dan.carpenter@oracle.com>
>>
>> [ Upstream commit 1376b0a2160319125c3a2822e8c09bd283cd8141 ]
>>
>> There is a '>' vs '<' typo so this loop is a no-op.
> 
> Thanks, but this driver seems to have lots of other bugs in 3.16, like
> it only ever accesses data[0] in this loop.  I don't think there's much
> point in applying just this one.  But if you think it's worth fixing
> then I can apply all the necessary fixes.
> 
> Ben.

It restores some basic functionality for daqp_ao_insn_write() that was 
broken.  The most common case to be handled is insn->n == 1, as that is 
what the comedi_data_write() function in the user-space Comedilib 
library sets.

However, it may be worth applying e024181b02ed ("staging: comedi: 
quatech_daqp_cs: fix bug in daqp_ao_insn_write()") and (with a small 
amount of backporting) e031642eccc0 ("staging: comedi: quatech_daqp_cs: 
use comedi_timeout() in ao (*insn_write)") before this one.  I'll append 
a patch series as replies to this email.

> 
>> Fixes: d35dcc89fc93 ("staging: comedi: quatech_daqp_cs: fix daqp_ao_insn_write()")
>> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>> Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
>> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> ---
>>   drivers/staging/comedi/drivers/quatech_daqp_cs.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/staging/comedi/drivers/quatech_daqp_cs.c b/drivers/staging/comedi/drivers/quatech_daqp_cs.c
>> index b3bbec0a0d23..f89a863ea04c 100644
>> --- a/drivers/staging/comedi/drivers/quatech_daqp_cs.c
>> +++ b/drivers/staging/comedi/drivers/quatech_daqp_cs.c
>> @@ -649,7 +649,7 @@ static int daqp_ao_insn_write(struct comedi_device *dev,
>>   	/* Make sure D/A update mode is direct update */
>>   	outb(0, dev->iobase + DAQP_AUX);
>>   
>> -	for (i = 0; i > insn->n; i++) {
>> +	for (i = 0; i < insn->n; i++) {
>>   		val = data[0];
>>   		val &= 0x0fff;
>>   		val ^= 0x0800;		/* Flip the sign */


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