Bug in p1_p2_rdb_pc? Caching-inhibited bit for initial L2 SRAM entry in TLB

From: "Pali Rohár" <pali@kernel.org>
To: Priyanka Jain <priyanka.jain@nxp.com>, Wolfgang Denk <wd@denx.de>,
	u-boot@lists.denx.de
Subject: Bug in p1_p2_rdb_pc? Caching-inhibited bit for initial L2 SRAM entry in TLB
Date: Tue, 5 Apr 2022 10:57:37 +0200	[thread overview]
Message-ID: <20220405085737.s34rfws7rg2zhe2n@pali> (raw)

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_rdb_pc/tlb.c#L99-104

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.