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@xxxxxxxxx Cc: Brian Norris <computersforpeace@xxxxxxxxx> Cc: Doug Berger <opendmb@xxxxxxxxx> Cc: Justin Chen <justinpopo6@xxxxxxxxx> Cc: Lee Jones <lee.jones@xxxxxxxxxx> Cc: Markus Mayer <mmayer@xxxxxxxxxxxx> Acked-by: Florian Fainelli <f.fainelli@xxxxxxxxx> Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> --- V2: - Removed the Fixes tag; - Added Florian's ACK - thanks! drivers/soc/bcm/brcmstb/pm/pm-arm.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/drivers/soc/bcm/brcmstb/pm/pm-arm.c b/drivers/soc/bcm/brcmstb/pm/pm-arm.c index 70ad0f3dce28..2a6adaa29596 100644 --- 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@xxxxxxxxx + */ static int brcmstb_pm_panic_notify(struct notifier_block *nb, unsigned long action, void *data) { -- 2.37.1
