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

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Message-ID: <dfe3fa28a907dedd263dbecb7b7ec96e7c3e27fa.camel@nvidia.com>
Date: Mon, 2 Dec 2024 10:09:13 +0000
From: Kartik Rajput <kkartik@...dia.com>
To: "thierry.reding@...il.com" <thierry.reding@...il.com>
CC: "jassisinghbrar@...il.com" <jassisinghbrar@...il.com>, Jon Hunter
	<jonathanh@...dia.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-tegra@...r.kernel.org"
	<linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v2] mailbox: tegra-hsp: Clear mailbox before using message

On Thu, 2024-11-28 at 11:22 +0100, Thierry Reding wrote:
> 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

Hi Thierry,

This patch fixes an issue with the Tegra RCE driver (which is available
as an external module), where it may process an IVC message before the
mailbox data register is cleared, resulting in a loss of IVC
notification.

I have posted v3 of this patch with an updated commit description.

Thanks & Regards,
Kartik