From a05e94bd5230a90eca2905495e764a0ad707c498 Mon Sep 17 00:00:00 2001 From: H Hartley Sweeten <hsweeten@visionengravers.com> Date: Mon, 24 Aug 2015 10:14:03 -0700 Subject: [PATCH] staging: comedi: usbduxfast: document strange ai maxdata The subdevice 'maxdata' is typically a mask of the valid bits that can be returned by a subdevice, (1 << bits) - 1. The analog inputs of this device have a resolution of 12-bits so the 'maxdata' should be 0x0fff. But, this hardware can produce a value of 0x1000 indicating an overflow from the ADC. The comedilib library's comedi_to_phys() function will then return NAN when this value is read from the hardware. Add a comment to clarify the strage 'maxdata' value. Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com> Reviewed-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- drivers/staging/comedi/drivers/usbduxfast.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/staging/comedi/drivers/usbduxfast.c b/drivers/staging/comedi/drivers/usbduxfast.c index 60f1c5e15a6a6..9e846b43f54ee 100644 --- a/drivers/staging/comedi/drivers/usbduxfast.c +++ b/drivers/staging/comedi/drivers/usbduxfast.c @@ -865,7 +865,7 @@ static int usbduxfast_attach_common(struct comedi_device *dev) s->do_cmdtest = usbduxfast_ai_cmdtest; s->do_cmd = usbduxfast_ai_cmd; s->cancel = usbduxfast_ai_cancel; - s->maxdata = 0x1000; + s->maxdata = 0x1000; /* 12-bit + 1 overflow bit */ s->range_table = &range_usbduxfast_ai_range; up(&devpriv->sem); -- 2.30.2