Hi Doug,
在 2016年11月10日 04:54, Doug Anderson 写道:
Hi,
On Mon, Nov 7, 2016 at 5:00 AM, William Wu <wulf@xxxxxxxxxxxxxx> wrote:
We found that the system crashed due to 480MHz output clock of
USB2 PHY was unstable after clock had been enabled by gpu module.
Theoretically, 1 millisecond is a critical value for 480MHz
output clock stable time, so we try to change the delay time
to 1.2 millisecond to avoid this issue.
Signed-off-by: William Wu <wulf@xxxxxxxxxxxxxx>
---
drivers/phy/phy-rockchip-inno-usb2.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/phy/phy-rockchip-inno-usb2.c b/drivers/phy/phy-rockchip-inno-usb2.c
index ecfd7d1..8f2d2b6 100644
--- a/drivers/phy/phy-rockchip-inno-usb2.c
+++ b/drivers/phy/phy-rockchip-inno-usb2.c
@@ -267,7 +267,7 @@ static int rockchip_usb2phy_clk480m_enable(struct clk_hw *hw)
return ret;
/* waitting for the clk become stable */
- mdelay(1);
+ udelay(1200);
Several people who have seen this patch have expressed concern that a
1.2 ms delay is pretty long for something that's supposed to be
"atomic" like a clk_enable(). Consider that someone might call
clk_enable() while interrupts are disabled and that a 1.2 ms interrupt
latency is not so great.
It seems like this clock should be moved to be enabled in "prepare"
and the "enable" should be a no-op. This is a functionality change,
but I don't think there are any real users for this clock at the
moment so it should be fine.
(of course, the 1 ms latency that existed before this patch was still
pretty bad, but ...)
Thanks a lot for your suggestion.
I agree with you. clk_enable() will call spin_lock_irqsave() to disable
interrupt, and we add
more than 1ms in clk_enable may cause big latency.
And according to clk_prepare() description:
In a simple case, clk_prepare can be used instead of clk_enable to
ungate a clk if the
operation may sleep. One example is a clk which is accessed over I2c.
So maybe we can remove the clock to clk_prepare.
Hi Heiko, Frank,
What do you think of it?
Best regards,
wulf
-Doug
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