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

[Eric Biggers <ebiggers@kernel.org>]

On Mon, Jul 08, 2024 at 01:26:30PM -0700, Eric Biggers wrote:
> 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.
> 

These same SMC calls can be found in the downstream source for other
Exynos-based SoCs.  I suspect that exynos_ufs_config_smu() should be removed,
and exynos_ufs_fmp_init() should run regardless of EXYNOS_UFS_OPT_UFSPR_SECURE.
It still would need to be tested, though, which I'm not able to do.  (And
especially as a cryptography feature, this *must* be tested...)  So for now I'm
going to make the FMP support conditional on EXYNOS_UFS_OPT_UFSPR_SECURE.

- Eric