[PATCH v2 0/2] mpfs: fix handling failed service requests

[PATCH v2 0/2] mpfs: fix handling failed service requests

[Conor Dooley]

From: Conor Dooley <conor.dooley@microchip.com>

As things stand, if a service request fails, we never know about it as
the status register is not read. This is quite obviously far from ideal,
as we would be reading garbage from the mailbox if a service was to
fail.

This pair of patches adds handling of the service status to both sides
of the mailbox implementation.

@Jassi, there should be no build, or really functional, dependency here
between patches. In the failing case, the buffer is allocated by the
service driver, so things will "work" just as badly as they did before
if only one of the patches is present. As a result, should be safe to do
the mailbox patch via your tree & the client via the soc tree.

Thanks,
Conor.

Changes since v1:
- Send the patches I meant to send, with an extraneous ; removed.

Conor Dooley (2):
  soc: microchip: mpfs: handle failed system service requests
  mailbox: mpfs: read the system controller's status

 drivers/mailbox/mailbox-mpfs.c              | 31 +++++++++++++++++++--
 drivers/soc/microchip/mpfs-sys-controller.c |  6 ++++
 2 files changed, 35 insertions(+), 2 deletions(-)

-- 
2.37.2

[PATCH v2 1/2] soc: microchip: mpfs: handle failed system service requests

[Conor Dooley]

From: Conor Dooley <conor.dooley@microchip.com>

If a service request fails, a non-zero, per-service error code will be
set. Since the individual service drivers may wish to handle things
differently, there's little point trying to do anything intelligent in
the system controller driver. Let the caller know that things went wrong
& leave the details of handling the error to it.

Fixes: d0054a470c33 ("soc: add microchip polarfire soc system controller")
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
 drivers/soc/microchip/mpfs-sys-controller.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/soc/microchip/mpfs-sys-controller.c b/drivers/soc/microchip/mpfs-sys-controller.c
index 6e20207b5756..539fc24b397d 100644
--- a/drivers/soc/microchip/mpfs-sys-controller.c
+++ b/drivers/soc/microchip/mpfs-sys-controller.c
@@ -52,6 +52,12 @@ int mpfs_blocking_transaction(struct mpfs_sys_controller *sys_controller, struct
 
 	mutex_unlock(&transaction_lock);
 
+	if (ret)
+		return ret;
+
+	if (msg->response->resp_status)
+		ret = -EIO;
+
 	return ret;
 }
 EXPORT_SYMBOL(mpfs_blocking_transaction);
-- 
2.37.2

[PATCH v2 2/2] mailbox: mpfs: read the system controller's status

[Conor Dooley]

From: Conor Dooley <conor.dooley@microchip.com>

Some services explicitly return an error code in their response, but
others rely on the system controller to set a status in its status
register. The meaning of the bits varies based on what service is
requested, so pass it back up to the driver that requested the service
in the first place. The field in the message struct already existed, but
was unused until now.

If the system controller is busy, in which case we should never actually
be in the interrupt handler, or if the service fails the mailbox itself
should not be read. Callers should check the status before operating on
the response.

Fixes: 83d7b1560810 ("mbox: add polarfire soc system controller mailbox")
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
 drivers/mailbox/mailbox-mpfs.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/drivers/mailbox/mailbox-mpfs.c b/drivers/mailbox/mailbox-mpfs.c
index cfacb3f320a6..6b99abac0b11 100644
--- a/drivers/mailbox/mailbox-mpfs.c
+++ b/drivers/mailbox/mailbox-mpfs.c
@@ -2,7 +2,7 @@
 /*
  * Microchip PolarFire SoC (MPFS) system controller/mailbox controller driver
  *
- * Copyright (c) 2020 Microchip Corporation. All rights reserved.
+ * Copyright (c) 2020-2022 Microchip Corporation. All rights reserved.
  *
  * Author: Conor Dooley <conor.dooley@microchip.com>
  *
@@ -23,6 +23,8 @@
 #define MAILBOX_REG_OFFSET		0x800u
 #define MSS_SYS_MAILBOX_DATA_OFFSET	0u
 #define SCB_MASK_WIDTH			16u
+#define SCB_STATUS_SHIFT		16u
+#define SCB_STATUS_MASK			GENMASK(31, SCB_STATUS_SHIFT)
 
 /* SCBCTRL service control register */
 
@@ -130,13 +132,38 @@ static void mpfs_mbox_rx_data(struct mbox_chan *chan)
 	struct mpfs_mbox *mbox = (struct mpfs_mbox *)chan->con_priv;
 	struct mpfs_mss_response *response = mbox->response;
 	u16 num_words = ALIGN((response->resp_size), (4)) / 4U;
-	u32 i;
+	u32 i, status;
 
 	if (!response->resp_msg) {
 		dev_err(mbox->dev, "failed to assign memory for response %d\n", -ENOMEM);
 		return;
 	}
 
+	/*
+	 * The status is stored in bits 31:16 of the SERVICES_SR register.
+	 * It is only valid when BUSY == 0.
+	 * We should *never* get an interrupt while the controller is
+	 * still in the busy state. If we do, something has gone badly
+	 * wrong & the content of the mailbox would not be valid.
+	 */
+	if (mpfs_mbox_busy(mbox)) {
+		dev_err(mbox->dev, "got an interrupt but system controller is busy\n");
+		response->resp_status = 0xDEAD;
+		return;
+	}
+
+	status = readl_relaxed(mbox->ctrl_base + SERVICES_SR_OFFSET);
+
+	/*
+	 * If the status of the individual servers is non-zero, the service has
+	 * failed. The contents of the mailbox at this point are not be valid,
+	 * so don't bother reading them. Set the status so that the driver
+	 * implementing the service can handle the result.
+	 */
+	response->resp_status = (status & SCB_STATUS_MASK) >> SCB_STATUS_SHIFT;
+	if (response->resp_status)
+		return;
+
 	if (!mpfs_mbox_busy(mbox)) {
 		for (i = 0; i < num_words; i++) {
 			response->resp_msg[i] =
-- 
2.37.2

Re: [PATCH v2 2/2] mailbox: mpfs: read the system controller's status

[Conor.Dooley]

On 18/11/2022 22:20, Conor Dooley wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> From: Conor Dooley <conor.dooley@microchip.com>
> 
> Some services explicitly return an error code in their response, but
> others rely on the system controller to set a status in its status
> register. The meaning of the bits varies based on what service is
> requested, so pass it back up to the driver that requested the service
> in the first place. The field in the message struct already existed, but
> was unused until now.
> 
> If the system controller is busy, in which case we should never actually
> be in the interrupt handler, or if the service fails the mailbox itself
> should not be read. Callers should check the status before operating on
> the response.
> 
> Fixes: 83d7b1560810 ("mbox: add polarfire soc system controller mailbox")
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> ---
>  drivers/mailbox/mailbox-mpfs.c | 31 +++++++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mailbox/mailbox-mpfs.c b/drivers/mailbox/mailbox-mpfs.c
> index cfacb3f320a6..6b99abac0b11 100644
> --- a/drivers/mailbox/mailbox-mpfs.c
> +++ b/drivers/mailbox/mailbox-mpfs.c
> @@ -2,7 +2,7 @@
>  /*
>   * Microchip PolarFire SoC (MPFS) system controller/mailbox controller driver
>   *
> - * Copyright (c) 2020 Microchip Corporation. All rights reserved.
> + * Copyright (c) 2020-2022 Microchip Corporation. All rights reserved.
>   *
>   * Author: Conor Dooley <conor.dooley@microchip.com>
>   *
> @@ -23,6 +23,8 @@
>  #define MAILBOX_REG_OFFSET             0x800u
>  #define MSS_SYS_MAILBOX_DATA_OFFSET    0u
>  #define SCB_MASK_WIDTH                 16u
> +#define SCB_STATUS_SHIFT               16u
> +#define SCB_STATUS_MASK                        GENMASK(31, SCB_STATUS_SHIFT)

*sigh* these macros aren't needed & generate some -Wmacro-redefined issues.
I'll do a v3 in a few days.