[PATCH] clk: allow clocks without parents to change rate

[PATCH] clk: allow clocks without parents to change rate

[Linus Walleij]

The clk_change_rate() code would dereference clk->parent
to get clk->parent->rate without first checking that clk->parent
was valid. This doesn't work if the clock is (A) a root clock
and (B) can change rate. Such is the case with a VCO clock
like the ICST which consequently crash like this without
this patch:

Unable to handle kernel NULL pointer dereference at virtual address 0000001c
pgd = c0004000
[0000001c] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT ARM
Modules linked in:
CPU: 0    Not tainted  (3.5.0-rc3-00003-g8156866-dirty #193)
PC is at clk_change_rate+0x34/0xd8
LR is at clk_change_rate+0x18/0xd8

Cc: stable at kernel.org
Cc: Mike Turquette <mturquette@linaro.org>
Cc: Ulf Hansson <ulf.hansson@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 drivers/clk/clk.c |   22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 687b00d..032d79c 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -854,14 +854,22 @@ static void clk_change_rate(struct clk *clk)
 
 	old_rate = clk->rate;
 
-	if (clk->ops->set_rate)
-		clk->ops->set_rate(clk->hw, clk->new_rate, clk->parent->rate);
+	if (clk->ops->set_rate) {
+		if (clk->parent)
+			clk->ops->set_rate(clk->hw, clk->new_rate,
+					clk->parent->rate);
+		else
+			clk->ops->set_rate(clk->hw, clk->new_rate, 0);
+	}
 
-	if (clk->ops->recalc_rate)
-		clk->rate = clk->ops->recalc_rate(clk->hw,
-				clk->parent->rate);
-	else
-		clk->rate = clk->parent->rate;
+	if (clk->ops->recalc_rate) {
+		if (clk->parent)
+			clk->rate = clk->ops->recalc_rate(clk->hw,
+							clk->parent->rate);
+		else
+			clk->rate = clk->ops->recalc_rate(clk->hw, 0);
+	} else
+		clk->rate = clk->parent ? clk->parent->rate : 0;
 
 	if (clk->notifier_count && old_rate != clk->rate)
 		__clk_notify(clk, POST_RATE_CHANGE, old_rate, clk->rate);
-- 
1.7.10.4

[PATCH] clk: allow clocks without parents to change rate

[Mike Turquette]

On 20120705-00:09, Linus Walleij wrote:
> The clk_change_rate() code would dereference clk->parent
> to get clk->parent->rate without first checking that clk->parent
> was valid. This doesn't work if the clock is (A) a root clock
> and (B) can change rate. Such is the case with a VCO clock
> like the ICST which consequently crash like this without
> this patch:
> 
> Unable to handle kernel NULL pointer dereference at virtual address 0000001c
> pgd = c0004000
> [0000001c] *pgd=00000000
> Internal error: Oops: 5 [#1] PREEMPT ARM
> Modules linked in:
> CPU: 0    Not tainted  (3.5.0-rc3-00003-g8156866-dirty #193)
> PC is at clk_change_rate+0x34/0xd8
> LR is at clk_change_rate+0x18/0xd8
> 
> Cc: stable at kernel.org
> Cc: Mike Turquette <mturquette@linaro.org>
> Cc: Ulf Hansson <ulf.hansson@stericsson.com>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Hi Linus,

This has been fixed in Pawell's patch, "clk: Check parent for NULL in
clk_change_rate".

Thanks,
Mike

> ---
>  drivers/clk/clk.c |   22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 687b00d..032d79c 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -854,14 +854,22 @@ static void clk_change_rate(struct clk *clk)
>  
>  	old_rate = clk->rate;
>  
> -	if (clk->ops->set_rate)
> -		clk->ops->set_rate(clk->hw, clk->new_rate, clk->parent->rate);
> +	if (clk->ops->set_rate) {
> +		if (clk->parent)
> +			clk->ops->set_rate(clk->hw, clk->new_rate,
> +					clk->parent->rate);
> +		else
> +			clk->ops->set_rate(clk->hw, clk->new_rate, 0);
> +	}
>  
> -	if (clk->ops->recalc_rate)
> -		clk->rate = clk->ops->recalc_rate(clk->hw,
> -				clk->parent->rate);
> -	else
> -		clk->rate = clk->parent->rate;
> +	if (clk->ops->recalc_rate) {
> +		if (clk->parent)
> +			clk->rate = clk->ops->recalc_rate(clk->hw,
> +							clk->parent->rate);
> +		else
> +			clk->rate = clk->ops->recalc_rate(clk->hw, 0);
> +	} else
> +		clk->rate = clk->parent ? clk->parent->rate : 0;
>  
>  	if (clk->notifier_count && old_rate != clk->rate)
>  		__clk_notify(clk, POST_RATE_CHANGE, old_rate, clk->rate);
> -- 
> 1.7.10.4
> 

[PATCH] clk: allow clocks without parents to change rate

[Linus Walleij]

On Thu, Jul 12, 2012 at 1:42 AM, Mike Turquette <mturquette@ti.com> wrote:

> This has been fixed in Pawell's patch, "clk: Check parent for NULL in
> clk_change_rate".

Yes, that'll probably work.

A small nitpick though:

I have slightly different semantics, Pawel's patch assigns zero if
parent is NULL, then use that as fallback, whereas I check for the
parent being NULL all the way. I was worried that the old sematics
could change like this:

So here it takes that:

+       if (clk->parent)
+               best_parent_rate = clk->parent->rate;
+

And I was cautious that if this changes the parent rate:

+               clk->ops->set_rate(clk->hw, clk->new_rate, best_parent_rate);

Then this passes the old parent rate to the recalc function:

+               clk->rate = clk->ops->recalc_rate(clk->hw, best_parent_rate);

It has no side-effects on my system but I worried about
others, so I just left the behaviour to re-read the rate from the parent
every time if possible.

Yours,
Linus Walleij

[PATCH] clk: allow clocks without parents to change rate

[Mike Turquette]

On 20120712-12:50, Linus Walleij wrote:
> On Thu, Jul 12, 2012 at 1:42 AM, Mike Turquette <mturquette@ti.com> wrote:
> 
> > This has been fixed in Pawell's patch, "clk: Check parent for NULL in
> > clk_change_rate".
> 
> Yes, that'll probably work.
> 
> A small nitpick though:
> 
> I have slightly different semantics, Pawel's patch assigns zero if
> parent is NULL, then use that as fallback, whereas I check for the
> parent being NULL all the way. I was worried that the old sematics
> could change like this:
> 
> So here it takes that:
> 
> +       if (clk->parent)
> +               best_parent_rate = clk->parent->rate;
> +
> 
> And I was cautious that if this changes the parent rate:
> 
> +               clk->ops->set_rate(clk->hw, clk->new_rate, best_parent_rate);
> 
> Then this passes the old parent rate to the recalc function:
> 
> +               clk->rate = clk->ops->recalc_rate(clk->hw, best_parent_rate);
> 
> It has no side-effects on my system but I worried about
> others, so I just left the behaviour to re-read the rate from the parent
> every time if possible.
> 

Thanks for looking into it.  I think for now let's keep what we have and
we'll patch it up if bugs are reported.

Thanks again,
Mike

> Yours,
> Linus Walleij