Hi Brian, On Mon, 23 Jul 2018 11:13:50 -0700 Brian Norris <computersforpeace at gmail.com> wrote: > Hello, > > I noticed this got merged, but I wanted to put my 2 cents in here: I wish you had replied to this thread when it was posted (more than 6 months ago). Reverting the patch now implies making some people unhappy because they'll have to resort to their old out-of-tree hacks :-(. > > On Wed, Dec 06, 2017 at 10:53:42AM +0800, Zhiqiang Hou wrote: > > From: Hou Zhiqiang <Zhiqiang.Hou at nxp.com> > > > > Restore the status to be compatible with legacy devices. > > Take Freescale eSPI boot for example, it copies (in 3 Byte > > addressing mode) the RCW and bootloader images from SPI flash > > without firing a reset signal previously, so the reboot command > > will fail without reseting the addressing mode of SPI flash. > > This patch implement .shutdown function to restore the status > > in reboot process, and add the same operation to the .remove > > function. > > We have previously rejected this patch multiple times, because the above > comment demonstrates a broken product. If we were to only support working HW parts, I fear Linux would not support a lot of HW (that's even more true when it comes to flashes :P). > You cannot guarantee that all > reboots will invoke the .shutdown() method -- what about crashes? What > about watchdog resets? IIUC, those will hit the same broken behavior, > and have unexepcted behavior in your bootloader. Yes, there are corner cases that are not addressed with this approach, but it still seems to improve things. Of course, that means the user should try to re-route all HW reset sources to SW ones (RESET input pin muxed to the GPIO controller, watchdog generating an interrupt instead of directly asserting the RESET output pin), which is not always possible, but even when it's not, isn't it better to have a setup that works fine 99% of the time instead of 50% of the time? > > I suppose one could argue for doing this in remove(), but AIUI you're > just papering over system bugs by introducing the shutdown() function > here. Thus, I'd prefer we drop the shutdown() method to avoid misleading > other users of this driver. I understand your point. But if the problem is about making sure people designing new boards get that right, why not complaining at probe time when things are wrong? I mean, spi_nor_restore() seems to only do something on very specific NORs (those on which a SW RESET does not resets the addressing mode). So, how about adding a flag that says "my board has the NOR HW RESET pin wired" (there would be a DT props to set that flag). Then you add a WARN_ON() when this flag is not set and a NOR chip impacted by this bug is detected. This way you make sure people are informed that they're doing something wrong, and for those who can't change their HW (because it's already widely deployed), you have a fix that improve things. Regards, Boris