On Sat, May 19, 2012 at 10:41 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Sat, 19 May 2012, Ming Lei wrote: > >> IMO, it is not a good idea. >> >> Firstly, after writing RESET on command register, the default value of >> CMD register >> should be restored to '00080000h (00080B00h if Asynchronous Schedule Park >> Capability is a one)'[1], and both 'Interrupt Threshold Control' and >> 'Park mode' has >> been set in ehci_init(), so using ehci->command after ehci_reset is correct. >> >> Secondly, remaining other bits from HW is not good since HW may be buggy >> and the default value after reset may be uncertain, and it is better >> to not depend >> on them. For some newer hardware, if the reserved fields are to be >> used, just do >> it in ehci_init like setting lpm bits. >> >> Finally, before the commit 3d9545cc375d117554a9b35dfddadf9189c62775( >> EHCI: maintain the ehci->command value properly), the ehci->command is used >> just directly in ehci_run and the other HW bits are not kept from HW, >> so it is better >> to be consistent as before to avoid introducing possible regression. >> >> [1], 4.1 Host Controller Initialization of EHCI Specification 1.0 >> >> > Would anyone like to code that up? >> >> Looks removing the line of 'ehci->command = ehci_readl(ehci, >> &ehci->regs->command);' in ehci_reset is OK. > > You have convinced me. In addition, my earlier reasoning didn't make > much sense. Nobody is developing new versions of EHCI these days; > they're all working on USB-3. > > I'll send in a new patch simply to remove that line of code. Or you > can, if you like. OK, I will send it out. Thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
