Hi Dan, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote on Tue, 1 Jun 2021 15:14:02 +0300: > On Thu, May 27, 2021 at 05:03:09PM +0200, Miquel Raynal wrote: > > Hi Colin, > > > > Colin King <colin.king@xxxxxxxxxxxxx> wrote on Thu, 27 May 2021 > > 15:50:48 +0100: > > > > > From: Colin Ian King <colin.king@xxxxxxxxxxxxx> > > > > > > Currently there are corner cases where spec_times is NULL and > > > chip->parameters.onfi or when best_mode is zero where ret is > > > > ^ > > something is missing here, the sentence is not clear > > > > > not assigned a value and an uninitialized return value can be > > > returned. Fix this by ensuring ret is initialized to -EINVAL. > > > > I don't see how this situation can happen. > > > > In both cases, no matter the value of best_mode, the for loop will > > always execute at least one time (mode 0) so ret will be populated. > > > > Maybe the robot does not know that best_mode cannot be negative and > > should be defined unsigned, but the current patch is invalid. > > > > People think list counter unsigned is a good idea, but it's a terrible > idea and has caused hundreds of bugs for me to fix/report over the > years. *grumble*. > > Anyway, I was revisiting this code because it showed up as a Smatch > warning and the bug appears to be real. > > best_mode = fls(chip->parameters.onfi->sdr_timing_modes) - 1; > > The "onfi->sdr_timing_modes" comes from the hardware in nand_onfi_detect() > and nothing checks that it is non-zero so "best_mode = fls(0) - 1;" is > negative and "ret" is uninitialized. In the ONFI specification, the sdr_timing_mode field is defined as follow: SDR timing mode support BIT VALUE MEANING 6-15 N/A Reserved (0) 5 1 supports timing mode 5 4 1 supports timing mode 4 3 1 supports timing mode 3 2 1 supports timing mode 2 1 1 supports timing mode 1 0 1 supports timing mode 0, shall be 1 IOW sdr_timing_modes *cannot* be 0, or it is a truly deep and crazily impacting hardware bug (so far I am not aware of any chip not returning the right timing mode 0 value). Hence my proposal to turn best_mode as unsigned. I honestly don't know what is the best option here and am fully open to other suggestions to silence the robot. Thanks, Miquèl
