On Tuesday 05 April 2022 10:57:37 Pali Rohár wrote:
Hello!
I suspect that there is a bug in board/freescale/p1_p2_rdb_pc/tlb.c code which configures TLB entry for initial L2 SRAM.
When L2 is 512 kB long (e.g. on P2020) then U-Boot *unsets* MAS2_I bit for first half of L2 and for second half of L2 U-Boot *sets* this bit.
See code: https://source.denx.de/u-boot/u-boot/-/blob/v2022.04/board/freescale/p1_p2_r...
I do not think that one part of L2 SRAM should be configured differently as second part. Therefore I think that this is a bug in U-Boot code.
Do you know is correct configuration of TLB entries for initial L2 SRAM?
MAS2_I is Caching-inhibited bit which is described as:
Caching-inhibited:
- 0 - Accesses to this page are considered cacheable.
- 1 - The page is considered caching-inhibited. All loads and stores to the page bypass the caches and are performed directly to main memory. A read or write to a caching-inhibited page affects only the memory element specified by the operation.
Hello! I found EREF: A Programmer’s Reference Manual for Freescale Power Architecture Processors Supports e500 core family (e500v1, e500v2, e500mc, e5500, e6500) e200 core family document at NXP web:
https://www.nxp.com/files-static/32bit/doc/ref_manual/EREF_RM.pdf
And section "Cache and MMU Architecture" in part 7.3.1.2.2 Unable to Lock Conditions (page 763) contains following information:
If no exceptions occur and no overlocking condition exists, an attempt to set a lock can fail if any of the following is true:
• The target address is marked cache-inhibited, or the storage attributes of the address uses a coherency protocol that does not support locking
So for me it looks like that L2 SRAM (which works at L2 with locked cache lines) should not set MA2_I (cache-inhibited) bit.
Any opinion? Or you do have some more information?