From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EF83D3D0905; Fri, 17 Jul 2026 07:57:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784275029; cv=none; b=ONdGLMv8bH5uAumK6zX4xXSu7LdccudItnt04M1BiczH1yoqNCBXqKPpexDIPIqctaagScJ8L1NB4bOZUBYALPnX+tTacXDW5tzuvKNcdZ0QYa26nfAUHy14ejVycBgz33MAD4jw+2eI+eb6kU8/5mdExM4AH//fyWnC/9ir3rI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784275029; c=relaxed/simple; bh=VYkib/2tRK0MBPMozIws6bs2eWmGsXy9ur+00gGPjsI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RBtfg1/7DoHDPCcc2CcPCXdncq7rUq0fOJAanYakxNIXHsR1VTnOcLEGAEk1Zp0T1A2sRo8LFwETRLEROwad2e0qN0h/Df91wGVnqoNssUGM5/yQHvCe972G2qW4MKQ0O6AUrY/w6cvsv97jTG8ei0xzcMmyHgDqv6CSwthrwWU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XjUYeDjw; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="XjUYeDjw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 593191F00A3D; Fri, 17 Jul 2026 07:57:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784275026; bh=l3gnAzfGUV0GNzGVkfZ16Z7U7vo259vFrwqGerv2HUE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=XjUYeDjwBeDv4RcNTGVLbpROQIk+JP+bX0Ou3MuG0qYgm4NA9APpkBey4CC5On7EN eK45M6ebVj5oYDAsBuCayDBwAld1jmxuf1KgCcvgOF7XNRMDkQCSDdlHAwKfkzU7iw 4kGGB7i2MD83NaWflGp9QgR31ORl5Yy7nDSAKBrANbnnwf83ARONjZ0D8/vBbm2kv5 h1gkShOj4fp0V3wDeQoMNE7y6UD8V8yJB7qUDnbYkOMl269QIDbjdeM4fLmtC9priR 9R11q6fP6GWz4eWMw9JGBaFdig3lsZsZmIMADe1H86tOGyr04Bdbgkh4075GFW9+zM Yh7OP3VZCWEbg== From: Sudeep Holla To: Jassi Brar , linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Sudeep Holla , Huisong Li Subject: [PATCH 3/3] mailbox: pcc: Fix command timeout due to missed interrupt Date: Fri, 17 Jul 2026 08:56:49 +0100 Message-ID: <20260717075649.467172-4-sudeep.holla@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260717075649.467172-1-sudeep.holla@kernel.org> References: <20260717075649.467172-1-sudeep.holla@kernel.org> Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Huisong Li PCC command execution can time out when a fast platform completes a transaction and signals the platform interrupt before pcc_send_data() marks the channel as in use. For shared platform interrupts, the type 3 handler uses chan_in_use to decide whether the interrupt belongs to the channel. If it observes false, it ignores the completion and the caller waits until timeout. Publish chan_in_use before ringing the doorbell. Use WRITE_ONCE() for the lockless flag update and READ_ONCE() in the interrupt handler when filtering shared interrupts. The following ordered MMIO accessor used for the doorbell keeps the earlier store visible before the platform is notified. Clear chan_in_use with WRITE_ONCE() when completing the transaction, matching the lockless flag protocol used by the interrupt and send paths. Fixes: 3db174e478cb ("mailbox: pcc: Support shared interrupt for multiple subspaces") Signed-off-by: Huisong Li Signed-off-by: Sudeep Holla --- drivers/mailbox/pcc.c | 39 ++++++++++++++++++++++++++------------- 1 file changed, 26 insertions(+), 13 deletions(-) diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c index 8dfa80b0a90f..7f99d4ab0129 100644 --- a/drivers/mailbox/pcc.c +++ b/drivers/mailbox/pcc.c @@ -91,12 +91,11 @@ struct pcc_chan_reg { * @plat_irq: platform interrupt * @type: PCC subspace type * @plat_irq_flags: platform interrupt flags - * @chan_in_use: this flag is used just to check if the interrupt needs - * handling when it is shared. Since only one transfer can occur - * at a time and mailbox takes care of locking, this flag can be - * accessed without a lock. Note: the type only support the - * communication from OSPM to Platform, like type3, use it, and - * other types completely ignore it. + * @chan_in_use: lockless flag used by initiator subspaces, such as type 3, + * to filter shared platform interrupts. Only one transfer can occur + * at a time, but the interrupt handler may sample the flag on another + * CPU, so all accesses must use READ_ONCE() or WRITE_ONCE(). + * Other subspace types ignore it. */ struct pcc_chan_info { struct pcc_mbox_chan chan; @@ -320,8 +319,13 @@ static irqreturn_t pcc_mbox_irq(int irq, void *p) if (pcc_chan_reg_read_modify_write(&pchan->plat_irq_ack)) return IRQ_NONE; + /* + * Master subspaces use this flag to filter shared interrupts. Use + * READ_ONCE() to sample the lockless flag written by pcc_send_data() + * on another CPU. + */ if (pchan->type == ACPI_PCCT_TYPE_EXT_PCC_MASTER_SUBSPACE && - !pchan->chan_in_use) + !READ_ONCE(pchan->chan_in_use)) return IRQ_NONE; if (!pcc_mbox_cmd_complete_check(pchan)) @@ -331,12 +335,12 @@ static irqreturn_t pcc_mbox_irq(int irq, void *p) return IRQ_NONE; /* - * Clear this flag after updating interrupt ack register and just - * before mbox_chan_received_data() which might call pcc_send_data() - * where the flag is set again to start new transfer. This is - * required to avoid any possible race in updatation of this flag. + * Clear this flag after updating the interrupt ack register and just + * before mbox_chan_received_data(), which might call pcc_send_data() + * and set the flag again to start a new transfer. Use WRITE_ONCE() + * for the lockless update observed by the send and interrupt paths. */ - pchan->chan_in_use = false; + WRITE_ONCE(pchan->chan_in_use, false); mbox_chan_received_data(chan, NULL); mbox_chan_txdone(chan, 0); @@ -464,9 +468,18 @@ static int pcc_send_data(struct mbox_chan *chan, void *data) if (ret) return ret; + /* + * Set chan_in_use before ringing the doorbell so a fast completion + * interrupt is not mistaken for a shared interrupt from another + * subspace. Use WRITE_ONCE() for the lockless flag update. The + * ordered MMIO accessor used to ring the doorbell keeps this store + * visible before the platform is notified. + */ + if (pchan->plat_irq > 0) + WRITE_ONCE(pchan->chan_in_use, true); ret = pcc_chan_reg_read_modify_write(&pchan->db); if (!ret && pchan->plat_irq > 0) - pchan->chan_in_use = true; + WRITE_ONCE(pchan->chan_in_use, false); return ret; } -- 2.43.0