Dear Liu Shengzhou-B36685,
-----Original Message----- From: Marek Vasut [mailto:marex@denx.de] Sent: Thursday, October 18, 2012 3:16 PM To: Liu Shengzhou-B36685 Cc: u-boot@lists.denx.de; Stefan Roese; agust@denx.de Subject: Re: [PATCH] powerpc/usb: fix bug of CPU hang when missing USB PHY clock
Dear Liu Shengzhou-B36685,
-----Original Message-----
+/* Check USB PHY clock valid */ +static int usb_phy_clk_valid(struct usb_ehci *ehci) {
- if ((!(in_be32(&ehci->control) & PHY_CLK_VALID)) &&
(!in_be32(&ehci->prictrl))) {(!A && !B) condition can certainly be done without the double negation ;-)
[Shengzhou] Yes, using !(A||B) is also okay:)
Good, you did your logic homework well. Now go one step further:
if (a || b)
return 1;
[Shengzhou] No, this doesn't work, b is 0 at initial time, but b is 1 at the second time, a is depend on the register PHY_CLK_VALID bit, We just want to check it at the first time and then think it is always valid after that, it's using a trick:)
Good point, I was just testing you of course ;-)
Best regards, Marek Vasut