* Matthijs van Duin <matthijsvanduin@xxxxxxxxx> [150405 16:53]: > Cortex-A8 errata doc states in its workaround for erratum 430973: > > > By default, the BTB Invalidate instruction is treated as a NOP on Cortex-A8. > > However, it is possible to enable the BTB Invalidate instruction such that it > > actually does a full invalidate of the BTB by setting the IBE bit (bit 6) in > > the CP15 Auxiliary Control Register. As a consequence of erratum 687067, the > > L1 System Array Debug Register should be cleared to 0 before the IBE bit is > > set using the following code sequence: > > MOV r1, #0 > > MCR p15, 0, r1, c15, c1, 0 ; write instruction data 0 register > > MRC p15, 0, R1, c1, c0, 1 ; read Aux Ctl Register > > ORR R1, R1 #(1 << 6) ; set IBE to 1 > > MCR p15, 0, R1, c1, c0, 1 ; write Aux Ctl Register > > The above code needs to be executed in Secure state. ARM Limited recommends > > that this code is added to the boot monitor. > > The 430973 workaround code in proc-v7.S will do absolutely nothing if > executed in non-secure state. Ditto for the 458693 workaround, and the > 460075 workaround should trigger an undefined instruction exception. > Maybe linux is started in secure mode on some targets and this code > was written for one of those? That's only for HS omaps, for those we currently only do it in the nokia_n900_legacy_init that calls rx51_secure_update_aux_cr. > I scanned DM814x secure ROM for any (ARM or Thumb) write to > Instruction L1 System Array Debug Register 0, but I found none, hence > my warning to watch out for erratum 687067. OK > Adding the full set of BTB invalidates while making sure IBE is > disabled on sufficiently recent Cortex-A8 revisions would be optimal > for the Cortex-A8. But, apparently (based on the description of the > ARMv7 CPUID registers) there are also processors which only require > BTB invalidates when code is modified, but not when context-switching, > so there may be performance considerations there... Attempting to summarize all that's been discussed.. It sounds like we need the following implemented: 1. For cortex-a8 revisions affected by 458693, we can do a custom cpu_v7_switch_mm function that always does flush BTAC/BTB. 2. For HS cortex-a8 processors other than n900 affected by 458693, we need to implement functions similar to rx51_secure_update_aux_cr, the bootrom on n900 is different from TI HS omaps so the SMC call numbering may be different. 3. For later cortex-a8 processors not affected by 458693, we need to clear IBE bit to avoid erratum 687067. Regards, Tony -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
