[prim, rom_ctrl] Remove S&P layer from data scrambling #20855
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For Ibex, this has to be disabled separately in a second PR, since we'll have to vendor the updated memory backdoor utils and the scrambling primitive into the ibex repository first. |
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As elaborated on lowRISC#20788, the S&P layer is disabled in the SRAM scrambling devices in order to improve error detection guarantees, interactions with ECC and timing. In order to minimize changes and keep the implementation around in case it is needed for byte parity at some point, we just set the NumDiffRounds parameter to zero for the modules that leverage prim_ram_1p_scr. In case of rom_ctrl, the functionality is removed entirely. Signed-off-by: Michael Schaffner <[email protected]>
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I am going ahead with this and merge it so that I can do the Ibex re-vendoring. |
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The S&P network on the data got removed in lowRISC#20855 as it negatively impacts the end-to-end integrity scheme but the PR forgot to update the documentation of the scrambling primitive (The SRAM_CTRL documentation got updated though). Since the additional diffusion might still be relevant for other implementations, it's worth to keep the documentation but explain that it is not enabled by default. Signed-off-by: Pirmin Vogel <[email protected]>
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The S&P network on the data got removed in #20855 as it negatively impacts the end-to-end integrity scheme but the PR forgot to update the documentation of the scrambling primitive (The SRAM_CTRL documentation got updated though). Since the additional diffusion might still be relevant for other implementations, it's worth to keep the documentation but explain that it is not enabled by default. Signed-off-by: Pirmin Vogel <[email protected]>
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As elaborated on #20788, the S&P layer is removed from data scrambling in order to improve error detection guarantees, interactions with ECC and timing.