Dear Liu Shengzhou-B36685, > > -----Original Message----- > > From: Marek Vasut [mailto:ma...@denx.de] > > Sent: Thursday, October 18, 2012 3:16 PM > > To: Liu Shengzhou-B36685 > > Cc: u-boot@lists.denx.de; Stefan Roese; ag...@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 _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot