I got it. Thanks for your help, vichy -----Original Message----- From: Alan Stern [mailto:[EMAIL PROTECTED] Sent: Monday, February 25, 2008 4:58 AM To: vichy Cc: linux-usb@vger.kernel.org Subject: Re: Question about port reset
On Sun, 24 Feb 2008, vichy wrote: > Dear all: > Below is a part of ehci_hub_control function in ehci-hub.c. > > /* force reset to complete */ > writel (temp & ~(PORT_RWC_BITS | PORT_RESET), > &ehci->regs->port_status [wIndex]); > Where PORT_RWC_BITS = (PORT_CSC | PORT_PEC | PORT_OCC) and if I interpret it > correctly, it will set PORT_CSC, PORT_PEC, PORT_OCC and PORT_RESET as 0. You do not interpret it correctly. The PORT_RWC_BITS are named that way because that are Read-and-Write-to-Clear. That is, when the computer writes a 1 to any of those bits, the effect is to set the bit to 0. Writing a 0 leaves the bit unchanged. > I can understand why we set PORT_RESET as 0, but why we set other 3 > parameters as 0, too. By including PORT_RWC_BITS in that statement we _avoid_ setting those bits to 0. Alan Stern - To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
