[S] Change in flashrom[main]: buspirate_spi: Add support for hiz output with pullups=off

[Dreg (Code Review)]

Dreg has uploaded this change for review. ( https://review.coreboot.org/c/flashrom/+/79299?usp=email )

Change subject: buspirate_spi: Add support for hiz output with pullups=off
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buspirate_spi: Add support for hiz output with pullups=off

When working with low-voltage chips, the internal 10k pull-ups of the Bus Pirate might be too high. In such cases, it's necessary to create an external pull-up using lower-value resistors. For this, you can use the ``hiz`` parameter.  This way, the Bus Pirate will operate as an open drain

Change-Id: I6d9909b23782ef3fcb1428fd127dae0d6b211855
Signed-off-by: Dreg 
---
M buspirate_spi.c
M doc/classic_cli_manpage.rst
2 files changed, 22 insertions(+), 2 deletions(-)

git pull ssh://review.coreboot.org:29418/flashrom refs/changes/99/79299/1

diff --git a/buspirate_spi.c b/buspirate_spi.c
index 72c28b0..7436d80 100644
--- a/buspirate_spi.c
+++ b/buspirate_spi.c
@@ -325,6 +325,7 @@
    int spispeed = 0x7;
    int serialspeed_index = -1;
    int ret = 0;
+	bool hiz = false;
    bool pullup = false;
    bool psu = false;
    bool aux = true;
@@ -368,6 +369,17 @@
    }
    free(tmp);

+	tmp = extract_programmer_param_str(cfg, "hiz");
+	if (tmp) {
+		if (strcasecmp("on", tmp) == 0)
+			hiz = true;
+		else if (strcasecmp("off", tmp) == 0)
+			; // ignore
+		else
+			msg_perr("Invalid hiz state, not using them.\n");
+	}
+	free(tmp);
+
    tmp = extract_programmer_param_str(cfg, "pullups");
    if (tmp) {
    	if (strcasecmp("on", tmp) == 0)
@@ -692,9 +704,9 @@

/* Set SPI config: output type, idle, clock edge, sample */
    bp_commbuf[0] = 0x80 | 0xa;
-	if (pullup) {
+	if (pullup || hiz) {
    	bp_commbuf[0] &= ~(1 << 3);
-		msg_pdbg("Pull-ups enabled, so using HiZ pin output! (Open-Drain mode)\n");
+		msg_pdbg("Pull-ups or HiZ enabled, so using HiZ pin output! (Open-Drain mode)\n");
    }
    ret = buspirate_sendrecv(bp_commbuf, 1, 1);
    if (ret)
diff --git a/doc/classic_cli_manpage.rst b/doc/classic_cli_manpage.rst
index 5d6b7ef..3157793 100644
--- a/doc/classic_cli_manpage.rst
+++ b/doc/classic_cli_manpage.rst
@@ -763,6 +763,14 @@
 where ``baud`` can be ``115200``, ``230400``, ``250000`` or ``2000000`` (``2M``).
 The default is ``2M`` baud for Bus Pirate hardware version 3.0 and greater, and 115200 otherwise.

+When working with low-voltage chips, the internal 10k pull-ups of the Bus Pirate might be too high. In such cases, it's 
+necessary to create an external pull-up using lower-value resistors. For this, you can use the ``hiz`` parameter. 
+This way, the Bus Pirate will operate as an open drain. Syntax is::
+
+        flashrom -p buspirate_spi:hiz=state
+
+where ``state`` can be ``on`` or ``off``.
+
 An optional pullups parameter specifies the use of the Bus Pirate internal pull-up resistors. This may be needed if you
 are working with a flash ROM chip that you have physically removed from the board. Syntax is::