Re: [PATCH net-next v22 1/2] mailbox/pcc: support mailbox management of the shared buffer

Re: [PATCH net-next v22 1/2] mailbox/pcc: support mailbox management of the shared buffer

[kernel test robot]

BCC: lkp@intel.com
CC: oe-kbuild-all@lists.linux.dev
In-Reply-To: <20250710191209.737167-2-admiyo@os.amperecomputing.com>
References: <20250710191209.737167-2-admiyo@os.amperecomputing.com>
TO: admiyo@os.amperecomputing.com
TO: Sudeep Holla <sudeep.holla@arm.com>
TO: Jassi Brar <jassisinghbrar@gmail.com>
TO: Robert Moore <robert.moore@intel.com>
TO: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
TO: Len Brown <lenb@kernel.org>
CC: netdev@vger.kernel.org
CC: linux-kernel@vger.kernel.org
CC: Jeremy Kerr <jk@codeconstruct.com.au>
CC: Matt Johnston <matt@codeconstruct.com.au>
CC: "David S . Miller" <davem@davemloft.net>
CC: Eric Dumazet <edumazet@google.com>
CC: Jakub Kicinski <kuba@kernel.org>
CC: Paolo Abeni <pabeni@redhat.com>
CC: Jonathan Cameron <Jonathan.Cameron@huawei.com>
CC: Huisong Li <lihuisong@huawei.com>

Hi,

kernel test robot noticed the following build warnings:

[auto build test WARNING on net-next/main]

url:    https://github.com/intel-lab-lkp/linux/commits/admiyo-os-amperecomputing-com/mailbox-pcc-support-mailbox-management-of-the-shared-buffer/20250711-031525
base:   net-next/main
patch link:    https://lore.kernel.org/r/20250710191209.737167-2-admiyo%40os.amperecomputing.com
patch subject: [PATCH net-next v22 1/2] mailbox/pcc: support mailbox management of the shared buffer
:::::: branch date: 27 hours ago
:::::: commit date: 27 hours ago
config: x86_64-randconfig-161-20250711 (https://download.01.org/0day-ci/archive/20250712/202507120609.Myazax08-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <error27@gmail.com>
| Closes: https://lore.kernel.org/r/202507120609.Myazax08-lkp@intel.com/

smatch warnings:
drivers/mailbox/pcc.c:498 pcc_send_data() error: uninitialized symbol 'ret'.

vim +/ret +498 drivers/mailbox/pcc.c

e332edef98ddac Adam Young         2025-07-10  476  
e332edef98ddac Adam Young         2025-07-10  477  
86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  478  /**
33350e6b1833b1 Ashwin Chaugule    2015-01-27  479   * pcc_send_data - Called from Mailbox Controller code. Used
33350e6b1833b1 Ashwin Chaugule    2015-01-27  480   *		here only to ring the channel doorbell. The PCC client
33350e6b1833b1 Ashwin Chaugule    2015-01-27  481   *		specific read/write is done in the client driver in
33350e6b1833b1 Ashwin Chaugule    2015-01-27  482   *		order to maintain atomicity over PCC channel once
33350e6b1833b1 Ashwin Chaugule    2015-01-27  483   *		OS has control over it. See above for flow of operations.
86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  484   * @chan: Pointer to Mailbox channel over which to send data.
33350e6b1833b1 Ashwin Chaugule    2015-01-27  485   * @data: Client specific data written over channel. Used here
33350e6b1833b1 Ashwin Chaugule    2015-01-27  486   *		only for debug after PCC transaction completes.
86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  487   *
86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  488   * Return: Err if something failed else 0 for success.
86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  489   */
86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  490  static int pcc_send_data(struct mbox_chan *chan, void *data)
86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  491  {
c45ded7e11352d Sudeep Holla       2021-09-17  492  	int ret;
bf18123e78f4d1 Sudeep Holla       2021-09-17  493  	struct pcc_chan_info *pchan = chan->con_priv;
e332edef98ddac Adam Young         2025-07-10  494  	struct acpi_pcct_ext_pcc_shared_memory __iomem *pcc_hdr;
e332edef98ddac Adam Young         2025-07-10  495  
e332edef98ddac Adam Young         2025-07-10  496  	if (pchan->chan.rx_alloc)
e332edef98ddac Adam Young         2025-07-10  497  		ret = pcc_write_to_buffer(chan, data);
e332edef98ddac Adam Young         2025-07-10 @498  	if (ret)
e332edef98ddac Adam Young         2025-07-10  499  		return ret;
8b0f57889843af Prakash, Prashanth 2016-02-17  500  
c45ded7e11352d Sudeep Holla       2021-09-17  501  	ret = pcc_chan_reg_read_modify_write(&pchan->cmd_update);
c45ded7e11352d Sudeep Holla       2021-09-17  502  	if (ret)
c45ded7e11352d Sudeep Holla       2021-09-17  503  		return ret;
c45ded7e11352d Sudeep Holla       2021-09-17  504  
e332edef98ddac Adam Young         2025-07-10  505  	pcc_hdr = pchan->chan.shmem;
e332edef98ddac Adam Young         2025-07-10  506  	if (ioread32(&pcc_hdr->flags) & PCC_CMD_COMPLETION_NOTIFY)
e332edef98ddac Adam Young         2025-07-10  507  		pchan->chan.irq_ack = true;
e332edef98ddac Adam Young         2025-07-10  508  
3db174e478cb0b Huisong Li         2023-08-01  509  	ret = pcc_chan_reg_read_modify_write(&pchan->db);
e332edef98ddac Adam Young         2025-07-10  510  
3db174e478cb0b Huisong Li         2023-08-01  511  	if (!ret && pchan->plat_irq > 0)
3db174e478cb0b Huisong Li         2023-08-01  512  		pchan->chan_in_use = true;
3db174e478cb0b Huisong Li         2023-08-01  513  
3db174e478cb0b Huisong Li         2023-08-01  514  	return ret;
86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  515  }
86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  516  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

[PATCH net-next v22 0/2] MCTP Over PCC Transport

[admiyo]

From: Linux Bot <linuxbot@amperecomputing.com>

This series adds support for the Management Control Transport Protocol (MCTP)
over the Platform Communication Channel (PCC) mechanism.

DMTF DSP:0292
https://www.dmtf.org/sites/default/files/standards/documents/DSP0292_1.0.0WIP50.pdf

MCTP defines a communication model intended to
facilitate communication between Management controllers
and other management controllers, and between Management
controllers and management devices

PCC is a mechanism for communication between components within
the  Platform.  It is a composed of shared memory regions,
interrupt registers, and status registers.

The MCTP over PCC driver makes use of two PCC channels. For
sending messages, it uses a Type 3 channel, and for receiving
messages it uses the paired Type 4 channel.  The device
and corresponding channels are specified via ACPI.

The first patch in the series implements a mechanism to allow the driver
to indicate whether an ACK should be sent back to the caller
after processing the interrupt.  This is an optional feature in
the PCC code, but has been made explicitly required in another driver.
The implementation here maintains the backwards compatibility of that
driver.

MCTP is a general purpose  protocol so  it would  be impossible to enumerate
all the use cases, but some of the ones that are most topical are attestation
and RAS support.  There are a handful of protocols built on top of MCTP, to
include PLDM and SPDM, both specified by the DMTF.

https://www.dmtf.org/sites/default/files/standards/documents/DSP0240_1.0.0.pdf
https://www.dmtf.org/sites/default/files/standards/documents/DSP0274_1.3.0.pd

SPDM entails various usages, including device identity collection, device
authentication, measurement collection, and device secure session establishment.

PLDM is more likely to be used  for hardware support: temperature, voltage, or
fan sensor control.

At least two companies have devices that can make use of the mechanism. One is
Ampere Computing, my employer.

The mechanism it uses is called Platform Communication Channels is part of the
ACPI spec: https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/14_Platform_Communications_Channel/Platform_Comm_Channel.html

Since it is a socket interface, the system administrator also has  the ability
to ignore an MCTP link that they do not want to enable.  This link would be visible
to the end user, but would not be usable.

If MCTP support is disabled in the Kernel, this driver would also be disabled.

PCC is based on a shared buffer and a set of I/O mapped memory locations that the
Spec calls registers.  This mechanism exists regardless of the existence of the
driver. Thus, if the user has the ability to map these  physical location to
virtual locations, they have the ability to drive the hardware.  Thus, there
is a security aspect to this mechanism that extends beyond the responsibilities
of the operating system.

If the hardware does not expose the PCC in the ACPI table, this device will never
be enabled.  Thus it is only an issue on hard that does support PCC.  In that case,
it is up to the remote controller to sanitize communication; MCTP will be exposed
as a socket interface, and userland can send any crafted packet it wants.  It would
thus also be incumbent on the hardware manufacturer to allow the end user to disable
MCTP over PCC communication if they did not want to expose it.

Previous implementations of the pcc version of the mailbox protocol assumed the
driver was directly managing the shared memory region.  This lead to duplicated
code and missed stpes of the PCC protocol. The first patch in this series makes
it possible for mailbox/pcc to manage the writing of the buffer prior to sending
messages.  It also fixes the notification of message transmission completion.

Previous Version:
https://lore.kernel.org/lkml/20250429222759.138627-1-admiyo@os.amperecomputing.com/

Changes in V22:
- Direct management of the shared buffer in the mailbox layer.
- Proper checking of command complete flag prior to writing to the buffer.

Changes in V21:
- Use existing constants PCC_SIGNATURE and PCC_CMD_COMPLETION_NOTIFY
- Check return code on call to send_data and drop packet if failed
- use sizeof(*mctp_pcc_header) etc,  instead of structs for resizing buffers
- simplify check for ares->type != PCC_DWORD_TYPE
- simply return result devm_add_action_or_reset
- reduce initializer for  mctp_pcc_lookup_context context = {};
- move initialization of mbox dev into mctp_pcc_initialize_mailbox
- minor spacing changes

Changes in V20:
- corrected typo in RFC version
- removed spurious space
- tx spin lock only controls access to shared memory buffer
- tx spin lock not eheld on error condition
- tx returns OK if skb can't be expanded

Changes in V19:
- Rebased on changes to PCC mailbox handling
- checks for cloned SKB prior to transmission
- converted doulbe slash comments to C comments

Changes in V18:
- Added Acked-By
- Fix minor spacing issue

Changes in V17:
- No new changes. Rebased on net-next post 6.13 release.

Changes in V16:
- do not duplicate cleanup after devm_add_action_or_reset calls

Changes in V15:
- corrected indentation formatting error
- Corrected TABS issue in MAINTAINER entry

Changes in V14:
- Do not attempt to unregister a netdev that is never registered
- Added MAINTAINER entry

Changes in V13:
- Explicitly Convert PCC header from little endian to machine native

Changes in V12:
- Explicitly use little endian conversion for PCC header signature
- Builds clean with make C=1

Changes in V11:
- Explicitly use little endian types for PCC header

Changes in V11:
- Switch Big Endian data types to machine local for PCC header
- use mctp specific function for registering netdev

Changes in V10:
- sync with net-next branch
- use dstats helper functions
- remove duplicate drop stat
- remove more double spaces

Changes in V9:
- Prerequisite patch for PCC mailbox has been merged
- Stats collection now use helper functions
- many double spaces reduced to single

Changes in V8:
- change 0 to NULL for pointer check of shmem
- add semi for static version of pcc_mbox_ioremap
- convert pcc_mbox_ioremap function to static inline when client code is not being built
- remove shmem comment from struct pcc_chan_info descriptor
- copy rx_dropped in mctp_pcc_net_stats
- removed trailing newline on error message
- removed double space in dev_dbg string
- use big endian for header members
- Fix use full spec ID in description
- Fix typo in file description
- Form the complete outbound message in the sk_buff

Changes in V7:
- Removed the Hardware address as specification is not published.
- Map the shared buffer in the mailbox and share the mapped region with the driver
- Use the sk_buff memory to prepare the message before copying to shared region

Changes in V6:
- Removed patch for ACPICA code that has merged
- Includes the hardware address in the network device
- Converted all device resources to devm resources
- Removed mctp_pcc_driver_remove function
- uses acpi_driver_module for initialization
- created helper structure for in and out mailboxes
- Consolidated code for initializing mailboxes in the add_device function
- Added specification references
- Removed duplicate constant PCC_ACK_FLAG_MASK
- Use the MCTP_SIGNATURE_LENGTH define
- made naming of header structs consistent
- use sizeof local variables for offset calculations
- prefix structure name to avoid potential clash
- removed unnecessary null initialization from acpi_device_id

Changes in V5
- Removed Owner field from ACPI module declaration
- removed unused next field from struct mctp_pcc_ndev
- Corrected logic reading  RX ACK flag.
- Added comment for struct pcc_chan_info field shmem_base_addr
- check against current mtu instead of max mtu for packet length\
- removed unnecessary lookups of pnd->mdev.dev

Changes in V4
- Read flags out of shared buffer to trigger ACK for Type 4 RX
- Remove list of netdevs and cleanup from devices only
- tag PCCT protocol headers as little endian
- Remove unused constants

Changes in V3
- removed unused header
- removed spurious space
- removed spurious semis after functiomns
- removed null assignment for init
- remove redundant set of device on skb
- tabify constant declarations
- added  rtnl_link_stats64 function
- set MTU to minimum to start
- clean up logic on driver removal
- remove cast on void * assignment
- call cleanup function directly
- check received length before allocating skb
- introduce symbolic constatn for ACK FLAG MASK
- symbolic constant for PCC header flag.
- Add namespace ID to PCC magic
- replaced readls with copy from io of PCC header
- replaced custom modules init and cleanup with ACPI version

Changes in V2

- All Variable Declarations are in reverse Xmass Tree Format
- All Checkpatch Warnings Are Fixed
- Removed Dead code
- Added packet tx/rx stats
- Removed network physical address.  This is still in
  disucssion in the spec, and will be added once there
  is consensus. The protocol can be used with out it.
  This also lead to the removal of the Big Endian
  conversions.
- Avoided using non volatile pointers in copy to and from io space
- Reorderd the patches to put the ACK check for the PCC Mailbox
  as a pre-requisite.  The corresponding change for the MCTP
  driver has been inlined in the main patch.
- Replaced magic numbers with constants, fixed typos, and other
  minor changes from code review.

Adam Young (2):
  mailbox/pcc: support mailbox management of the shared buffer
  mctp pcc: Implement MCTP over PCC Transport

 MAINTAINERS                 |   5 +
 drivers/mailbox/pcc.c       |  91 +++++++++-
 drivers/net/mctp/Kconfig    |  13 ++
 drivers/net/mctp/Makefile   |   1 +
 drivers/net/mctp/mctp-pcc.c | 346 ++++++++++++++++++++++++++++++++++++
 include/acpi/pcc.h          |  19 ++
 6 files changed, 472 insertions(+), 3 deletions(-)
 create mode 100644 drivers/net/mctp/mctp-pcc.c

-- 
2.43.0

[PATCH net-next v22 1/2] mailbox/pcc: support mailbox management of the shared buffer

[admiyo]

From: Adam Young <admiyo@os.amperecomputing.com>

Define a new, optional, callback that allows the driver to
specify how the return data buffer is allocated.  If that callback
is set,  mailbox/pcc.c is now responsible for reading from and
writing to the PCC shared buffer.

This also allows for proper checks of the Commnand complete flag
between the PCC sender and receiver.

For Type 4 channels, initialize the command complete flag prior
to accepting messages.

Since the mailbox does not know what memory allocation scheme
to use for response messages, the client now has an optional
callback that allows it to allocate the buffer for a response
message.

When an outbound message is written to the buffer, the mailbox
checks for the flag indicating the client wants an tx complete
notification via IRQ.  Upon reciept of the interrupt It will
pair it with the outgoing message. The expected use is to
free the kernel memory buffer for the previous outgoing message.

Signed-off-by: Adam Young <admiyo@os.amperecomputing.com>
---
 drivers/mailbox/pcc.c | 91 +++++++++++++++++++++++++++++++++++++++++--
 include/acpi/pcc.h    | 19 +++++++++
 2 files changed, 107 insertions(+), 3 deletions(-)

diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
index f6714c233f5a..2932c26aaf62 100644
--- a/drivers/mailbox/pcc.c
+++ b/drivers/mailbox/pcc.c
@@ -306,6 +306,22 @@ static void pcc_chan_acknowledge(struct pcc_chan_info *pchan)
 		pcc_chan_reg_read_modify_write(&pchan->db);
 }
 
+static void *write_response(struct pcc_chan_info *pchan)
+{
+	struct pcc_header pcc_header;
+	void *buffer;
+	int data_len;
+
+	memcpy_fromio(&pcc_header, pchan->chan.shmem,
+		      sizeof(pcc_header));
+	data_len = pcc_header.length - sizeof(u32) + sizeof(struct pcc_header);
+
+	buffer = pchan->chan.rx_alloc(pchan->chan.mchan->cl, data_len);
+	if (buffer != NULL)
+		memcpy_fromio(buffer, pchan->chan.shmem, data_len);
+	return buffer;
+}
+
 /**
  * pcc_mbox_irq - PCC mailbox interrupt handler
  * @irq:	interrupt number
@@ -317,6 +333,7 @@ static irqreturn_t pcc_mbox_irq(int irq, void *p)
 {
 	struct pcc_chan_info *pchan;
 	struct mbox_chan *chan = p;
+	void *handle = NULL;
 
 	pchan = chan->con_priv;
 
@@ -340,7 +357,14 @@ static irqreturn_t pcc_mbox_irq(int irq, void *p)
 	 * required to avoid any possible race in updatation of this flag.
 	 */
 	pchan->chan_in_use = false;
-	mbox_chan_received_data(chan, NULL);
+
+	if (pchan->chan.rx_alloc)
+		handle = write_response(pchan);
+
+	if (pchan->chan.irq_ack)
+		mbox_chan_txdone(chan, 0);
+
+	mbox_chan_received_data(chan, handle);
 
 	pcc_chan_acknowledge(pchan);
 
@@ -384,9 +408,22 @@ pcc_mbox_request_channel(struct mbox_client *cl, int subspace_id)
 	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)
+		goto err;
+
+	/* This indicates that the channel is ready to accept messages.
+	 * This needs to happen after the channel has registered
+	 * its callback. There is no access point to do that in
+	 * the mailbox API. That implies that the mailbox client must
+	 * have set the allocate callback function prior to
+	 * sending any messages.
+	 */
+	if (pchan->type == ACPI_PCCT_TYPE_EXT_PCC_SLAVE_SUBSPACE)
+		pcc_chan_reg_read_modify_write(&pchan->cmd_update);
+
+	return pcc_mchan;
 
+err:
 	mbox_free_channel(chan);
 	return ERR_PTR(-ENXIO);
 }
@@ -417,6 +454,27 @@ void pcc_mbox_free_channel(struct pcc_mbox_chan *pchan)
 }
 EXPORT_SYMBOL_GPL(pcc_mbox_free_channel);
 
+static int pcc_write_to_buffer(struct mbox_chan *chan, void *data)
+{
+	struct pcc_chan_info *pchan = chan->con_priv;
+	struct pcc_mbox_chan *pcc_mbox_chan = &pchan->chan;
+	struct pcc_header *pcc_header = data;
+	/* The PCC header length includes the command field
+	 * but not the other values from the header.
+	 */
+	int len = pcc_header->length - sizeof(u32) + sizeof(struct pcc_header);
+	u64 val;
+
+	pcc_chan_reg_read(&pchan->cmd_complete, &val);
+	if (!val) {
+		pr_info("%s pchan->cmd_complete not set", __func__);
+		return -1;
+	}
+	memcpy_toio(pcc_mbox_chan->shmem,  data, len);
+	return 0;
+}
+
+
 /**
  * pcc_send_data - Called from Mailbox Controller code. Used
  *		here only to ring the channel doorbell. The PCC client
@@ -433,18 +491,44 @@ static int pcc_send_data(struct mbox_chan *chan, void *data)
 {
 	int ret;
 	struct pcc_chan_info *pchan = chan->con_priv;
+	struct acpi_pcct_ext_pcc_shared_memory __iomem *pcc_hdr;
+
+	if (pchan->chan.rx_alloc)
+		ret = pcc_write_to_buffer(chan, data);
+	if (ret)
+		return ret;
 
 	ret = pcc_chan_reg_read_modify_write(&pchan->cmd_update);
 	if (ret)
 		return ret;
 
+	pcc_hdr = pchan->chan.shmem;
+	if (ioread32(&pcc_hdr->flags) & PCC_CMD_COMPLETION_NOTIFY)
+		pchan->chan.irq_ack = true;
+
 	ret = pcc_chan_reg_read_modify_write(&pchan->db);
+
 	if (!ret && pchan->plat_irq > 0)
 		pchan->chan_in_use = true;
 
 	return ret;
 }
 
+
+static bool pcc_last_tx_done(struct mbox_chan *chan)
+{
+	struct pcc_chan_info *pchan = chan->con_priv;
+	u64 val;
+
+	pcc_chan_reg_read(&pchan->cmd_complete, &val);
+	if (!val)
+		return false;
+	else
+		return true;
+}
+
+
+
 /**
  * pcc_startup - Called from Mailbox Controller code. Used here
  *		to request the interrupt.
@@ -490,6 +574,7 @@ static const struct mbox_chan_ops pcc_chan_ops = {
 	.send_data = pcc_send_data,
 	.startup = pcc_startup,
 	.shutdown = pcc_shutdown,
+	.last_tx_done = pcc_last_tx_done,
 };
 
 /**
diff --git a/include/acpi/pcc.h b/include/acpi/pcc.h
index 840bfc95bae3..b5414572912a 100644
--- a/include/acpi/pcc.h
+++ b/include/acpi/pcc.h
@@ -17,6 +17,25 @@ struct pcc_mbox_chan {
 	u32 latency;
 	u32 max_access_rate;
 	u16 min_turnaround_time;
+
+	/* Set to true When a message is sent that has the flag
+	 * set that the client requests an Interrupt
+	 * indicating that the transmission is complete.
+	 */
+	bool irq_ack;
+	/* Optional callback that allows the driver
+	 * to allocate the memory used for receiving
+	 * messages.  The return value is the location
+	 * inside the buffer where the mailbox should write the data.
+	 */
+	void *(*rx_alloc)(struct mbox_client *cl,  int size);
+};
+
+struct pcc_header {
+	u32 signature;
+	u32 flags;
+	u32 length;
+	u32 command;
 };
 
 /* Generic Communications Channel Shared Memory Region */
-- 
2.43.0

Re: [PATCH net-next v22 1/2] mailbox/pcc: support mailbox management of the shared buffer

[kernel test robot]

Hi,

kernel test robot noticed the following build warnings:

[auto build test WARNING on net-next/main]

url:    https://github.com/intel-lab-lkp/linux/commits/admiyo-os-amperecomputing-com/mailbox-pcc-support-mailbox-management-of-the-shared-buffer/20250711-031525
base:   net-next/main
patch link:    https://lore.kernel.org/r/20250710191209.737167-2-admiyo%40os.amperecomputing.com
patch subject: [PATCH net-next v22 1/2] mailbox/pcc: support mailbox management of the shared buffer
config: i386-randconfig-014-20250711 (https://download.01.org/0day-ci/archive/20250711/202507111440.1zQdhxpr-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250711/202507111440.1zQdhxpr-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202507111440.1zQdhxpr-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/mailbox/pcc.c:496:6: warning: variable 'ret' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
     496 |         if (pchan->chan.rx_alloc)
         |             ^~~~~~~~~~~~~~~~~~~~
   drivers/mailbox/pcc.c:498:6: note: uninitialized use occurs here
     498 |         if (ret)
         |             ^~~
   drivers/mailbox/pcc.c:496:2: note: remove the 'if' if its condition is always true
     496 |         if (pchan->chan.rx_alloc)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~
     497 |                 ret = pcc_write_to_buffer(chan, data);
   drivers/mailbox/pcc.c:492:9: note: initialize the variable 'ret' to silence this warning
     492 |         int ret;
         |                ^
         |                 = 0
   1 warning generated.


vim +496 drivers/mailbox/pcc.c

   476	
   477	
   478	/**
   479	 * pcc_send_data - Called from Mailbox Controller code. Used
   480	 *		here only to ring the channel doorbell. The PCC client
   481	 *		specific read/write is done in the client driver in
   482	 *		order to maintain atomicity over PCC channel once
   483	 *		OS has control over it. See above for flow of operations.
   484	 * @chan: Pointer to Mailbox channel over which to send data.
   485	 * @data: Client specific data written over channel. Used here
   486	 *		only for debug after PCC transaction completes.
   487	 *
   488	 * Return: Err if something failed else 0 for success.
   489	 */
   490	static int pcc_send_data(struct mbox_chan *chan, void *data)
   491	{
   492		int ret;
   493		struct pcc_chan_info *pchan = chan->con_priv;
   494		struct acpi_pcct_ext_pcc_shared_memory __iomem *pcc_hdr;
   495	
 > 496		if (pchan->chan.rx_alloc)
   497			ret = pcc_write_to_buffer(chan, data);
   498		if (ret)
   499			return ret;
   500	
   501		ret = pcc_chan_reg_read_modify_write(&pchan->cmd_update);
   502		if (ret)
   503			return ret;
   504	
   505		pcc_hdr = pchan->chan.shmem;
   506		if (ioread32(&pcc_hdr->flags) & PCC_CMD_COMPLETION_NOTIFY)
   507			pchan->chan.irq_ack = true;
   508	
   509		ret = pcc_chan_reg_read_modify_write(&pchan->db);
   510	
   511		if (!ret && pchan->plat_irq > 0)
   512			pchan->chan_in_use = true;
   513	
   514		return ret;
   515	}
   516	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH net-next v22 1/2] mailbox/pcc: support mailbox management of the shared buffer

[Dan Carpenter]

Hi,

kernel test robot noticed the following build warnings:

url:    https://github.com/intel-lab-lkp/linux/commits/admiyo-os-amperecomputing-com/mailbox-pcc-support-mailbox-management-of-the-shared-buffer/20250711-031525
base:   net-next/main
patch link:    https://lore.kernel.org/r/20250710191209.737167-2-admiyo%40os.amperecomputing.com
patch subject: [PATCH net-next v22 1/2] mailbox/pcc: support mailbox management of the shared buffer
config: x86_64-randconfig-161-20250711 (https://download.01.org/0day-ci/archive/20250712/202507120609.Myazax08-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
| Closes: https://lore.kernel.org/r/202507120609.Myazax08-lkp@intel.com/

smatch warnings:
drivers/mailbox/pcc.c:498 pcc_send_data() error: uninitialized symbol 'ret'.

vim +/ret +498 drivers/mailbox/pcc.c

86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  490  static int pcc_send_data(struct mbox_chan *chan, void *data)
86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  491  {
c45ded7e11352d Sudeep Holla       2021-09-17  492  	int ret;
bf18123e78f4d1 Sudeep Holla       2021-09-17  493  	struct pcc_chan_info *pchan = chan->con_priv;
e332edef98ddac Adam Young         2025-07-10  494  	struct acpi_pcct_ext_pcc_shared_memory __iomem *pcc_hdr;
e332edef98ddac Adam Young         2025-07-10  495  
e332edef98ddac Adam Young         2025-07-10  496  	if (pchan->chan.rx_alloc)
e332edef98ddac Adam Young         2025-07-10  497  		ret = pcc_write_to_buffer(chan, data);

Hi Adam!  :)

ret is uninitialized on the else path.

e332edef98ddac Adam Young         2025-07-10 @498  	if (ret)
e332edef98ddac Adam Young         2025-07-10  499  		return ret;
8b0f57889843af Prakash, Prashanth 2016-02-17  500  
c45ded7e11352d Sudeep Holla       2021-09-17  501  	ret = pcc_chan_reg_read_modify_write(&pchan->cmd_update);
c45ded7e11352d Sudeep Holla       2021-09-17  502  	if (ret)
c45ded7e11352d Sudeep Holla       2021-09-17  503  		return ret;
c45ded7e11352d Sudeep Holla       2021-09-17  504  
e332edef98ddac Adam Young         2025-07-10  505  	pcc_hdr = pchan->chan.shmem;
e332edef98ddac Adam Young         2025-07-10  506  	if (ioread32(&pcc_hdr->flags) & PCC_CMD_COMPLETION_NOTIFY)
e332edef98ddac Adam Young         2025-07-10  507  		pchan->chan.irq_ack = true;
e332edef98ddac Adam Young         2025-07-10  508  
3db174e478cb0b Huisong Li         2023-08-01  509  	ret = pcc_chan_reg_read_modify_write(&pchan->db);
e332edef98ddac Adam Young         2025-07-10  510  
3db174e478cb0b Huisong Li         2023-08-01  511  	if (!ret && pchan->plat_irq > 0)
3db174e478cb0b Huisong Li         2023-08-01  512  		pchan->chan_in_use = true;
3db174e478cb0b Huisong Li         2023-08-01  513  
3db174e478cb0b Huisong Li         2023-08-01  514  	return ret;
86c22f8c9a3b71 Ashwin Chaugule    2014-11-12  515  }

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https://github.com/intel/lkp-tests/wiki

Re: [PATCH net-next v22 1/2] mailbox/pcc: support mailbox management of the shared buffer

[Adam Young]

Internal review discovered an error

On 7/10/25 15:12, admiyo@os.amperecomputing.com wrote:
> +	if (pchan->chan.rx_alloc)
> +		ret = pcc_write_to_buffer(chan, data);

This is the wrong check. The rx_alloc is expected to be used  for the 
type4, and the will be called from the type 3.

Going to add an explicit flag instead.


> +	pcc_hdr = pchan->chan.shmem;
> +	if (ioread32(&pcc_hdr->flags) & PCC_CMD_COMPLETION_NOTIFY)
> +		pchan->chan.irq_ack = true;

This flag can be removed and replaced  with a check of the value in the 
original buffer, which is held in chan->current_req.


Updated version of the patch series to follow.