On Thu, Apr 02, 2020 at 01:13:24PM +0100, Guillaume Tucker wrote: > On 01/04/2020 17:31, Russell King - ARM Linux admin wrote: > > On Wed, Apr 01, 2020 at 05:08:03PM +0100, Guillaume Tucker wrote: > >> Allow setting the number of cycles for RAM reads in the pl310 cache > >> controller L2 auxiliary control register mask (bits 0-2) since it > >> needs to be changed in software. This only affects exynos4210 and > >> exynos4412 as they use the pl310 cache controller. > >> > >> With the mask used until now, the following warnings were generated, > >> the 2nd one being a pr_alert(): > >> > >> L2C: platform modifies aux control register: 0x02070000 -> 0x3e470001 > >> L2C: platform provided aux values permit register corruption. > >> > >> This latency cycles value has always been set in software in spite of > >> the warnings. Keep it this way but clear the alert message about > >> register corruption to acknowledge it is a valid thing to do. > > > > This is telling you that you are doing something you should not be > > doing. The L2C controller should be configured by board firmware > > first and foremost, because if, for example, u-boot makes use of the > > L2 cache, or any other pre-main kernel code (in other words, > > decompressor) the setup of the L2 controller will be wrong. > > > > So, NAK. > > OK thanks, I guess I misinterpreted the meaning of the error > message. It's really saying that the register value was not the > right one before the kernel tried to change it. Next step for me > is to look into U-Boot. The message "L2C: platform provided aux values permit register corruption." means that bits are set in both the mask and the value fields. Since the new value is calculated as: old = register value; new = old & mask; new |= val; If bits are set in both "mask" and "val" for a multi-bit field, the value ending up in the field may not be what is intended. Consider a 5-bit field set initially to 10101, and the requested value is 01000 with a mask of 11111. What you end up with is not 01000, but 11101. Hence, register corruption. It is not possible to easily tell whether the mask and values refer to a multi-bit field or not, so the mere fact that bits are set in both issues the alert. The message "L2C: platform modifies aux control register ..." means that you're trying to modify the value of the auxiliary control register, which brings with it the problems I stated in my previous email; platform configuration of the L2C must be done by firmware and not the kernel for the reasons I've set out. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 10.2Mbps down 587kbps up
