Messages in this thread |  | | Date | Fri, 14 Feb 2014 11:49:45 +0000 | From | Ian Abbott <> | Subject | Re: [PATCH] Staging: comedi: clean up conditional statement in addi_apci_3xxx.c |
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On 2014-02-13 18:25, Hartley Sweeten wrote: > On Wednesday, February 12, 2014 8:29 PM, Chase Southwood wrote: >> In this if-else conditional statement, if (chan < 16), but >> (data[0] == INSN_CONFIG_DIO_QUERY), the function does not return early, >> but the else-branch does not get executed either. As a result, mask >> would be used uninitialized in the next line. What we want here is if >> (chan < 16) and (data[0] != INSN_CONFIG_DIO_QUERY), return an error, but >> in every other case, initialize mask and then proceed. Found by a static >> checker. >> >> Signed-off-by: Chase Southwood <chase.southwood@yahoo.com> >> --- >> drivers/staging/comedi/drivers/addi_apci_3xxx.c | 12 +++++------- >> 1 file changed, 5 insertions(+), 7 deletions(-) >> >> diff --git a/drivers/staging/comedi/drivers/addi_apci_3xxx.c b/drivers/staging/comedi/drivers/addi_apci_3xxx.c >> index ceadf8e..04c5153 100644 >> --- a/drivers/staging/comedi/drivers/addi_apci_3xxx.c >> +++ b/drivers/staging/comedi/drivers/addi_apci_3xxx.c >> @@ -688,13 +688,11 @@ static int apci3xxx_dio_insn_config(struct comedi_device *dev, >> * Port 1 (channels 8-15) are always outputs >> * Port 2 (channels 16-23) are programmable i/o >> */ >> - if (chan < 16) { >> - if (data[0] != INSN_CONFIG_DIO_QUERY) >> - return -EINVAL; >> - } else { >> - /* changing any channel in port 2 changes the entire port */ >> - mask = 0xff0000; >> - } >> + if ((chan < 16) && (data[0] != INSN_CONFIG_DIO_QUERY)) >> + return -EINVAL; >> + >> + /* changing any channel in port 2 changes the entire port */ >> + mask = 0xff0000; >> >> ret = comedi_dio_insn_config(dev, s, insn, data, mask); >> if (ret) > > The uninitialized mask when chan < 16 is an issue. But your patch is not quite correct. > > The original code was intending to limit the valid instructions for channels < 16 to only > INSN_CONFIG_DIO_QUERY. These channels have fixed directions: 0-7 (port 0) are > always inputs and 8-15 (port 1) are always outputs. Channels 16-23 (port 2) have > programmable direction but changing any channel effects the entire port, that's > what the 0xff0000 mask is for. > > Changing the mask to 0xff0000 for any chanspec will result in the INSN_CONFIG_DIO_QUERY > instruction returning the direction of port 2 regardless of what the chanspec is. > > The "right" fix would be: > 1) Default the mask to 0 so that comedi_dio_insn_config() will use a chan_mask > based on the chanspec for the INSN_CONFIG_DIO_QUERY instruction. > 2) Ignore all instructions except INSN_CONFIG_DIO_QUERY when the chan < 16. > 3) Modify the mask for chan >= 16 when the instruction is not INSN_CONFIG_DIO_QUERY > so that the INSN_CONFIG_DIO_{INPUT,OUTPUT} instructions update the entire > port.
Agreed, but another question is why does comedi_dio_insn_config() in drivers.c need to look at the supplied mask at all for INSN_CONFIG_DIO_QUERY?
-- -=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@mev.co.uk> )=- -=( Tel: +44 (0)161 477 1898 FAX: +44 (0)161 718 3587 )=-
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