Turquette, Mike had written, on 04/21/2010 04:21 PM, the following:
[...]
/**
+ * voltscale_adaptive_body_bias - controls ABB ldo during voltage scaling
+ * @target_volt: target voltage determines if ABB ldo is active or bypassed
+ *
+ * Adaptive Body-Bias is a technique in all OMAP silicon that uses the 45nm
+ * process. ABB can boost voltage in high OPPs for silicon with weak
+ * characteristics (forward Body-Bias) as well as lower voltage in low OPPs
+ * for silicon with strong characteristics (Reverse Body-Bias).
+ *
+ * Only Foward Body-Bias for operating at high OPPs is implemented below, per
+ * recommendations from silicon team.
+ * Reverse Body-Bias for saving power in active cases and sleep cases is not
+ * yet implemented.
+ * OMAP4 hardward also supports ABB ldo, but no recommendations have been made
+ * to implement it yet.
+ */
+int voltscale_adaptive_body_bias(unsigned long target_volt)
+{
+ u32 sr2en_enabled;
+ int timeout;
+ int sr2_wtcnt_value;
+
+ /* calculate SR2_WTCNT_VALUE settling time */
+ sr2_wtcnt_value = (ABB_MAX_SETTLING_TIME *
+ (clk_get_rate("sys_ck") / 1000000) / 8);
+
+ /* has SR2EN been enabled previously? */
+ sr2en_enabled = (prm_read_mod_reg(OMAP3430_GR_MOD,
+ OMAP3_PRM_LDO_ABB_CTRL_OFFSET) &
+ OMAP3630_SR2EN);
+
+ /* select fast, nominal or slow OPP for ABB ldo */
+ /* FIXME: include OMAP4 once recommendations are complete */
+ if (cpu_is_omap3630() && (target_volt >= 1350000)) {
You are creating two steps to decide if you apply or not FBB.
Here and also bellow (omap voltage scale). Would it make sense to bind it
per opp? I mean just a flag on opp dat then you apply or not based on that flag.
Same for RBB.
Eduardo,
Thanks for reviewing.
There has been some offline discussion about the best way to handle the
the relationship between FBB enable flags and OPPs:
1) extend OPP table
2) piggyback on Thara's SR hwmod structures
This probably won't work given Paul's review comments
3) other wacky stuff
After some discussion about the best way to do this I will definitely
lose the duplicate checks and replace with some nice table look-up.
Extending the OPP table is gross for OMAP2 and OMAP3430. Piggybacking
on SR stuff is just a hack and there is no real relationship between ABB
ldo and SR. The crux of the issue is how to relate FBB enable flags to
OPP table. hwmod? Ideas on this are very welcome.
might be a good idea for using
I vote for 2) omap_volt_data in voltage.c and using the flag there.
1) is a bad idea as ABB is not present in older silicon and opp table
should ideally be independent of silicon and contain only common data..
[...]
--
Regards,
Nishanth Menon
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