On Tue, Feb 13, 2018 at 01:14:14PM +0100, Philipp Rossak 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: Since when is it there? > 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 > > Fixes: 04940631b8d2 ("rtc: ac100: Add clk output support") Should it be sent to stable? > Signed-off-by: Philipp Rossak <embed3d@xxxxxxxxx> > --- > > Changes in v2: > * add tag Fixes: ... to commit message > * add comment to if statement why we are doing this check > > drivers/rtc/rtc-ac100.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/drivers/rtc/rtc-ac100.c b/drivers/rtc/rtc-ac100.c > index 8ff9dc3fe5bf..ba73201d8cc1 100644 > --- a/drivers/rtc/rtc-ac100.c > +++ b/drivers/rtc/rtc-ac100.c > @@ -183,7 +183,17 @@ 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; > + > + /* > + * We purposefully left open the possibility to use the clock > + * from the codec side but it is not implemented right now. > + * Thus we need to check if the parent exists. > + */ > + if (!parent) > + continue; > + > + prate = clk_hw_get_rate(parent); clk_hw_get_num_parents should return the exact number of parents, which is going to be 1 if you only have one parent, like all DTS seems to have. If not, then it should be explained in the comment and / or fixed properly. Maxime -- Maxime Ripard, Bootlin (formerly Free Electrons) Embedded Linux and Kernel engineering http://bootlin.com
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