On Tue, Feb 13, 2018 at 5:07 AM, Philipp Rossak <embed3d@xxxxxxxxx> wrote: > This patch fixes a bug, that prevents the Allwinner A83T and the A80 > from a successful boot. You can find the shortend trace below: > > Unable to handle kernel NULL pointer dereference at virtual address > 00000000 > pgd = (ptrval) > [00000000] *pgd=00000000 > Internal error: Oops: 5 [#1] SMP ARM > Modules linked in: > CPU: 0 PID: 49 Comm: kworker/0:1 Not tainted 4.15.0-10190-gb89e32ccd1be #2 > Hardware name: Allwinner sun8i Family > Workqueue: events deferred_probe_work_func > PC is at clk_hw_get_rate+0x0/0x34 > LR is at ac100_clkout_determine_rate+0x48/0x19c > > [ ... ] > > (clk_hw_get_rate) from (ac100_clkout_determine_rate+0x48/0x19c) > (ac100_clkout_determine_rate) from (clk_core_set_rate_nolock+0x3c/0x1a0) > (clk_core_set_rate_nolock) from (clk_set_rate+0x30/0x88) > (clk_set_rate) from (of_clk_set_defaults+0x200/0x364) > (of_clk_set_defaults) from (platform_drv_probe+0x18/0xb0) > > To fix that bug, we first check if the return of the > clk_hw_get_parent_by_index is non zero. If it is zero we skip that > clock parent. > > The BUG report could be found here: https://lkml.org/lkml/2018/2/10/198 > Please add the tag: Fixes: 04940631b8d2 ("rtc: ac100: Add clk output support") > Signed-off-by: Philipp Rossak <embed3d@xxxxxxxxx> > --- > drivers/rtc/rtc-ac100.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/drivers/rtc/rtc-ac100.c b/drivers/rtc/rtc-ac100.c > index 8ff9dc3fe5bf..820ce6fb9d34 100644 > --- a/drivers/rtc/rtc-ac100.c > +++ b/drivers/rtc/rtc-ac100.c > @@ -183,7 +183,12 @@ static int ac100_clkout_determine_rate(struct clk_hw *hw, > > for (i = 0; i < num_parents; i++) { > struct clk_hw *parent = clk_hw_get_parent_by_index(hw, i); > - unsigned long tmp, prate = clk_hw_get_rate(parent); > + unsigned long tmp, prate; > + > + if (!parent) > + continue; There should be a comment on why this is happening, i.e. we purposefully left open the possibility of the clock from the codec side missing. Otherwise I think the clk subsystem doesn't expect this to happen, which is why there are no checks like this anywhere. ChenYu > + > + prate = clk_hw_get_rate(parent); > > tmp = ac100_clkout_round_rate(hw, req->rate, prate); > > -- > 2.11.0 >