linux-kernel - Re: [PATCH v2] mailbox: tegra-hsp: Clear mailbox before using message

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Message-ID: <hofrxrz5qvxohlvxme4brhng6rrs7s6wwoqwnu3smjbbonhwh4@xajjliw474v6>
Date: Thu, 28 Nov 2024 11:22:31 +0100
From: Thierry Reding <thierry.reding@...il.com>
To: Kartik Rajput <kkartik@...dia.com>
Cc: jassisinghbrar@...il.com, jonathanh@...dia.com, 
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mailbox: tegra-hsp: Clear mailbox before using message

On Thu, Nov 28, 2024 at 02:29:30PM +0530, Kartik Rajput wrote:
> From: Pekka Pessi <ppessi@...dia.com>
> 
> Some clients depend on mailbox being empty before processing the
> message. On RT kernel, the thread processing the message may be on
> different CPU or running with higher priority than the interrupt
> handler thread and they may act on the message before mailbox is
> emptied.
> 
> Fixes: 8f585d14030d ("mailbox: tegra-hsp: Add tegra_hsp_sm_ops")
> Fixes: 74c20dd0f892 ("mailbox: tegra-hsp: Add 128-bit shared mailbox support")
> Cc: stable@...r.kernel.org
> Signed-off-by: Pekka Pessi <ppessi@...dia.com>
> Signed-off-by: Kartik Rajput <kkartik@...dia.com>
> ---
> v1 -> v2:
> 	* Added "Fixes:" tag in the commit message.
> 	* Made similar change for 128-bit shared mailboxes.
> ---
>  drivers/mailbox/tegra-hsp.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)

Do we know what exactly "some clients" means? I know that TCU uses this
shared mailbox and sometimes it does go into a weird state where it can
loose characters, so I wonder if that's one case that would be fixed by
this.

Not strictly a requirement, but it would be good if we can give a good
description of a case where this helps.

Thierry

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