linux-kernel - Re: [PATCH 5/6] mailbox: pcc: Initialize SHMEM before binding the channel with the client

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Message-ID: <ffcaebef-9575-48ab-bf81-a570bb93e3c4@amperemail.onmicrosoft.com>
Date: Fri, 17 Oct 2025 12:59:49 -0400
From: Adam Young <admiyo@...eremail.onmicrosoft.com>
To: Sudeep Holla <sudeep.holla@....com>, linux-acpi@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Adam Young <admiyo@...amperecomputing.com>,
 Robbie King <robbiek@...ghtlabs.com>, Huisong Li <lihuisong@...wei.com>,
 Jassi Brar <jassisinghbrar@...il.com>,
 Cristian Marussi <cristian.marussi@....com>
Subject: Re: [PATCH 5/6] mailbox: pcc: Initialize SHMEM before binding the
 channel with the client

Tested-by: Adam Young <admiyo@...amperecomputing.com>

On 10/16/25 15:08, Sudeep Holla wrote:
> The PCC channel's shared memory region must be set up before the
> mailbox controller binds the channel with the client, as the binding
> process may trigger client operations like startup() that may rely on
> SHMEM being initialized.
>
> Reorder the setup sequence to ensure the shared memory is ready before
> binding. Initialize and map the PCC shared memory (SHMEM) prior to
> calling mbox_bind_client() so that clients never observe an uninitialized
> or NULL SHMEM during bind-time callbacks or early use in startup().
>
> This makes the PCC mailbox channel bring-up order consistent and
> eliminates a race between SHMEM setup and client binding.
>
> This will be needed in channel startup to clear/acknowledge any pending
> interrupts before enabling them.
>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>   drivers/mailbox/pcc.c | 18 ++++++++++--------
>   1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
> index 33bd2d05704b..2829ec51b47f 100644
> --- a/drivers/mailbox/pcc.c
> +++ b/drivers/mailbox/pcc.c
> @@ -378,18 +378,20 @@ pcc_mbox_request_channel(struct mbox_client *cl, int subspace_id)
>   		return ERR_PTR(-EBUSY);
>   	}
>   
> -	rc = mbox_bind_client(chan, cl);
> -	if (rc)
> -		return ERR_PTR(rc);
> -
>   	pcc_mchan = &pchan->chan;
>   	pcc_mchan->shmem = acpi_os_ioremap(pcc_mchan->shmem_base_addr,
>   					   pcc_mchan->shmem_size);
> -	if (pcc_mchan->shmem)
> -		return pcc_mchan;
> +	if (!pcc_mchan->shmem)
> +		return ERR_PTR(-ENXIO);
>   
> -	mbox_free_channel(chan);
> -	return ERR_PTR(-ENXIO);
> +	rc = mbox_bind_client(chan, cl);
> +	if (rc) {
> +		iounmap(pcc_mchan->shmem);
> +		pcc_mchan->shmem = NULL;
> +		return ERR_PTR(rc);
> +	}
> +
> +	return pcc_mchan;
>   }
>   EXPORT_SYMBOL_GPL(pcc_mbox_request_channel);
>   
>