Re: [PATCH v2 6/6] scsi: ufs: exynos: Add support for Flash Memory Protector (FMP)

[Eric Biggers <ebiggers@kernel.org>]

Hi Peter,

On Thu, Jul 04, 2024 at 02:26:05PM +0100, Peter Griffin wrote:
> Do you know how these FMP registers (FMPSECURITY0 etc) relate to the
> UFSPR* registers set in the existing exynos_ufs_config_smu()? The
> UFS_LINK spec talks about UFSPR(FMP), so I had assumed the FMP support
> would be writing these same registers but via SMC call.
> 
> I think by the looks of things
> 
> #define UFSPRSECURITY 0x010
> #define UFSPSBEGIN0 0x200
> #define UFSPSEND0 0x204
> #define UFSPSLUN0 0x208
> #define UFSPSCTRL0 0x20C
> 
> relates to the following registers in gs101 spec
> 
> FMPSECURITY0 0x0010
> FMPSBEGIN0 0x2000
> FMPSEND0 0x2004
> FMPSLUN0 0x2008
> FMPSCTRL0 0x200C
> 
> And the SMC calls your calling set those same registers as
> exynos_ufs_config_smu() function. Although it is hard to be certain as
> I don't have access to the firmware code. Certainly the comment below
> about FMPSECURITY0 implies that :)
> 
> With that in mind I think exynos_ufs_fmp_init() function in this patch
> needs to be better integrated with the EXYNOS_UFS_OPT_UFSPR_SECURE
> flag and the existing exynos_ufs_config_smu() function that is
> currently just disabling decryption on platforms where it can access
> the UFSPR(FMP) regs via mmio.

I think that is all correct.  For some reason, on gs101 the FMP registers are
not accessible by the "normal world", and SMC calls need to be used instead.
The sequences of SMC calls originated from Samsung's Linux driver code for FMP.
So I know they are the magic incantations that are needed, but I don't have
access to the source code or documentation for them.  It does seem clear that
one of the things they must do is write the needed values to the FMP registers.

I'd hope that these same SMC calls also work on Exynos-based SoCs that do make
the FMP registers accessible to the "normal world", and therefore they can just
be used on all Exynos-based SoCs and ufs-exynos won't need two different code
paths.  But I don't have a way to confirm this myself.  Until someone is able to
confirm this, I think we need to make the FMP support depend on
EXYNOS_UFS_OPT_UFSPR_SECURE so that it doesn't conflict with
exynos_ufs_config_smu() which runs when !EXYNOS_UFS_OPT_UFSPR_SECURE.

- Eric