soc: bcm: brcmstb: Document panic notifier action and remove useless header

The panic notifier of this driver is very simple code-wise, just a
memory write to a special position with some numeric code. But this
is not clear from the semantic point-of-view, and there is no public
documentation about that either.

After discussing this in the mailing-lists [0] and having Florian
explained it very well, document that in the code for the future
generations asking the same questions. Also, while at it, remove
a useless header.

[0] https://lore.kernel.org/lkml/781cafb0-8d06-8b56-907a-5175c2da196a@gmail.com

Cc: Brian Norris <computersforpeace@gmail.com>
Cc: Doug Berger <opendmb@gmail.com>
Cc: Justin Chen <justinpopo6@gmail.com>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Markus Mayer <mmayer@broadcom.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Link: https://lore.kernel.org/r/20220719195325.402745-5-gpiccoli@igalia.com
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

diff --git a/drivers/soc/bcm/brcmstb/pm/pm-arm.c b/drivers/soc/bcm/brcmstb/pm/pm-arm.c
index d6b30d5..7643c9a 100644 (file)
--- a/drivers/soc/bcm/brcmstb/pm/pm-arm.c
+++ b/drivers/soc/bcm/brcmstb/pm/pm-arm.c
@@ -25,7 +25,6 @@
 #include <linux/kernel.h>
 #include <linux/memblock.h>
 #include <linux/module.h>
-#include <linux/notifier.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
 #include <linux/panic_notifier.h>
@@ -664,7 +663,20 @@ static void __iomem *brcmstb_ioremap_match(const struct of_device_id *matches,
 
        return of_io_request_and_map(dn, index, dn->full_name);
 }
-
+/*
+ * The AON is a small domain in the SoC that can retain its state across
+ * various system wide sleep states and specific reset conditions; the
+ * AON DATA RAM is a small RAM of a few words (< 1KB) which can store
+ * persistent information across such events.
+ *
+ * The purpose of the below panic notifier is to help with notifying
+ * the bootloader that a panic occurred and so that it should try its
+ * best to preserve the DRAM contents holding that buffer for recovery
+ * by the kernel as opposed to wiping out DRAM clean again.
+ *
+ * Reference: comment from Florian Fainelli, at
+ * https://lore.kernel.org/lkml/781cafb0-8d06-8b56-907a-5175c2da196a@gmail.com
+ */
 static int brcmstb_pm_panic_notify(struct notifier_block *nb,
                unsigned long action, void *data)
 {