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nb/intel/sandybridge: Clarify command timing calculation 

Command timing is the absolute value of the most negative `pi_coding`
value across all ranks, or zero if there are no negative values. Use the
MAX() macro to ease proving that `cmd_delay` can never be negative, and
then drop the always-false underflow check.

The variable type for `cmd_delay` still needs to be signed because of
the comparisons with `pi_coding`, which is a signed value. Using an
unsigned type would result in undefined and also undesired behavior.

Change-Id: I714d3cf57d0f62376a1107af63bcd761f952bc3a
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49320
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
This commit is contained in:
Angel Pons 2021-01-12 01:21:24 +01:00 committed by Patrick Georgi
parent 0a7d99c089
commit 7519ca42b5
1 changed files with 3 additions and 8 deletions
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11
src/northbridge/intel/sandybridge/raminit_common.c
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@ -938,16 +938,11 @@ void program_timings(ramctr_timing *ctrl, int channel)
u32 clk_logic_dly = 0;
/*
* Apply command delay if desired setting is negative. Find the
* most negative value: 'cmd_delay' will be the absolute value.
* Compute command timing as abs() of the most negative PI code
* across all ranks. Use zero if none of the values is negative.
*/
FOR_ALL_POPULATED_RANKS {
if (cmd_delay < -ctrl->timings[channel][slotrank].pi_coding)
cmd_delay = -ctrl->timings[channel][slotrank].pi_coding;
}
if (cmd_delay < 0) {
printk(BIOS_ERR, "C%d command delay underflow: %d\n", channel, cmd_delay);
cmd_delay = 0;
cmd_delay = MAX(cmd_delay, -ctrl->timings[channel][slotrank].pi_coding);
}
if (cmd_delay > CCC_MAX_PI) {
printk(BIOS_ERR, "C%d command delay overflow: %d\n", channel, cmd_delay);