On Wed, Nov 04, 2020 at 10:49:18AM +0000, Ian Abbott wrote: > On 02/11/2020 11:16, Ian Abbott wrote: > > On 02/11/2020 10:25, Ian Abbott wrote: > > > On 29/10/2020 14:18, Ian Abbott wrote: > > > > Commit eddd2a4c675c ("staging: comedi: cb_pcidas: refactor > > > > write_calibration_bitstream()") inadvertently removed one of the > > > > `udelay(1)` calls when writing to the calibration register in > > > > `cb_pcidas_calib_write()`. Reinstate the delay. It may seem strange > > > > that the delay is placed before the register write, but this function is > > > > called in a loop so the extra delay can make a difference. > > > > > > > > This _might_ solve reported issues reading analog inputs on a > > > > PCIe-DAS1602/16 card where the analog input values "were scaled in a > > > > strange way that didn't make sense". On the same hardware running a > > > > system with a 3.13 kernel, and then a system with a 4.4 kernel, but with > > > > the same application software, the system with the 3.13 kernel was fine, > > > > but the one with the 4.4 kernel exhibited the problem. Of the 90 > > > > changes to the driver between those kernel versions, this change looked > > > > like the most likely culprit. > > > > > > Actually, I've realized that this patch will have no effect on the > > > PCIe-DAS1602/16 card because it uses a different driver - > > > cb_pcimdas, not cb_pcidas. > > > > But that's also confusing because PCIe-DAS1602/16 was not supported > > until the 3.19 kernel! I know the reported has both PCI-DAS1602/16 and > > PCIe-DAS1602/16 cards (supported by cb_pcidas and cb_pcimdas > > respectively), so there could have been some mix-up in the reporting. > > Mystery solved. The reporter had a mixture of PCIe-DAS1602/16 and > PCIM-DAS1602/16 cards (not PCI-DAS1602/16). Both of those are supported by > the "cb_pcimdas" driver (not "cb_pcidas"), although the PCIe card was not > supported until the 3.19 kernel (by commit 4e3d14af1286). Testing with the > 3.13 kernel was done with the PCIM card. > > The "strange scaling" was due to a change in the ranges reported for the > analog input subdevice in the 4.1 kernel (by commit c7549d770a27). Before > then, it just reported a single dummy range [0, 1000000] with no units > (converted to [0.0, 1.0] with no units by comedilib). Afterwards, it > reported four different voltage ranges (either unipolar or bipolar, > depending in a status bit tied to a physical switch). The reporter's > application code was using the reported range to scale the raw values to a > voltage (using comedilib functions), but because the reported range was > bogus, the application code was performing additional scaling (outside of > comedilib). The application code can be changed to check whether the device > is reporting a proper voltage range or the old, bogus range, and behave > accordingly. > > > > Greg, you might as well drop this patch if you haven't already > > > applied it, since it was only a hunch that it fixed a problem. > > That's still the case, although it won't do any harm if applied (apart from > the incorrect patch description). I'll leave it dropped :) thanks, greg k-h _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel