[PATCH v4] rtc: ac100: Fix ac100 determine rate bug

[Alexandre Belloni]

On 26/02/2018 at 22:19:01 +0100, Philipp Rossak wrote:
> This patch fixes a bug, that prevents the Allwinner A83T and the A80
> from a successful boot.
> 
> The bug is there since v4.16-rc1 and appeared after the clk branch was
> merged.
> 
> 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
> 
> Fixes: 04940631b8d2 ("rtc: ac100: Add clk output support")
> 
> Signed-off-by: Philipp Rossak <embed3d at gmail.com>
> ---
> 
> Changes in v4:
> 	* add more information to the comment
> Changes in v3:
> 	* add information when the bug appeared 
> 	* make the comment more clear
> 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 | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
Applied, thanks.

-- 
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com