[v2,04/13] soc: bcm: brcmstb: Document panic notifier action and remove useless header

Commit Message

Guilherme G. Piccoli July 19, 2022, 7:53 p.m. UTC

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/[e-mail]

Cc: Brian Norris <[e-mail]>
Cc: Doug Berger <[e-mail]>
Cc: Justin Chen <[e-mail]>
Cc: Lee Jones <[e-mail]>
Cc: Markus Mayer <[e-mail]>
Acked-by: Florian Fainelli <[e-mail]>
Signed-off-by: Guilherme G. Piccoli <[e-mail]>

---

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(-)

Comments

Florian Fainelli July 20, 2022, 11 p.m. UTC | #1

On Tue, 19 Jul 2022 16:53:17 -0300, "Guilherme G. Piccoli" <[e-mail]> wrote:
> 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/[e-mail]
> 
> Cc: Brian Norris <[e-mail]>
> Cc: Doug Berger <[e-mail]>
> Cc: Justin Chen <[e-mail]>
> Cc: Lee Jones <[e-mail]>
> Cc: Markus Mayer <[e-mail]>
> Acked-by: Florian Fainelli <[e-mail]>
> Signed-off-by: Guilherme G. Piccoli <[e-mail]>
> 
> ---

Applied to https://github.com/Broadcom/stblinux/commits/drivers/next, thanks!
--
Florian

Guilherme G. Piccoli July 21, 2022, 1:17 p.m. UTC | #2

On 20/07/2022 20:00, Florian Fainelli wrote:
> [...]
> 
> Applied to https://github.com/Broadcom/stblinux/commits/drivers/next, thanks!
> --
> Florian

Thanks Florian =)

Patch

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/[e-mail]
+ */
 static int brcmstb_pm_panic_notify(struct notifier_block *nb,
 		unsigned long action, void *data)
 {