linux-kernel - [PATCH 1/2] bus: mhi: host: Add quirk framework and initial quirk

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Date:   Fri, 14 Apr 2023 13:57:18 -0600
From:   Jeffrey Hugo <quic_jhugo@...cinc.com>
To:     <mani@...nel.org>
CC:     <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        <mhi@...ts.linux.dev>, Jeffrey Hugo <quic_jhugo@...cinc.com>
Subject: [PATCH 1/2] bus: mhi: host: Add quirk framework and initial quirk

Some devices might require special handling due to flawed implementations
or other reasons. Implement a quirk framework to handle these situations.

Implement the first quirk in this framework -
MHI_QUIRK_SOC_HW_VERSION_UNRELIABLE

The MHI spec indicates that the MHI device must initialize the
SOC_HW_VERSION register before the link to the MHI device is initialized.
The MHI host implementation uses this register as a quick check to see if
the device can be accessed early in the init process.

If an implementation is flawed, and does not properly initialize this
register, it may contain garbage data. In the case of PCIe, the value
0xFFFFFFFF has special meaning and can indicate that the link is down.
Such an implementation may cause MHI to believe the device cannot be
initialized.

Allow such controller to indicate that the host implementation should not
access this register, and handle the access accordingly during MHI init.

Signed-off-by: Jeffrey Hugo <quic_jhugo@...cinc.com>
Reviewed-by: Carl Vanderlip <quic_carlv@...cinc.com>
---
 drivers/bus/mhi/host/init.c | 13 +++++++++----
 include/linux/mhi.h         | 18 ++++++++++++++++++
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/drivers/bus/mhi/host/init.c b/drivers/bus/mhi/host/init.c
index f72fcb6..2731b78 100644
--- a/drivers/bus/mhi/host/init.c
+++ b/drivers/bus/mhi/host/init.c
@@ -891,6 +891,8 @@ static int parse_config(struct mhi_controller *mhi_cntrl,
 	if (config->m2_no_db)
 		mhi_cntrl->db_access &= ~MHI_PM_M2;
 
+	mhi_cntrl->quirks = config->quirks;
+
 	return 0;
 
 error_ev_cfg:
@@ -982,10 +984,13 @@ int mhi_register_controller(struct mhi_controller *mhi_cntrl,
 	}
 
 	/* Read the MHI device info */
-	ret = mhi_read_reg(mhi_cntrl, mhi_cntrl->regs,
-			   SOC_HW_VERSION_OFFS, &soc_info);
-	if (ret)
-		goto err_destroy_wq;
+	if (mhi_cntrl->quirks & MHI_QUIRK_SOC_HW_VERSION_UNRELIABLE) {
+		soc_info = 0;
+	else {
+		ret = mhi_read_reg(mhi_cntrl, mhi_cntrl->regs, SOC_HW_VERSION_OFFS, &soc_info);
+		if (ret)
+			goto err_destroy_wq;
+	}
 
 	mhi_cntrl->family_number = FIELD_GET(SOC_HW_VERSION_FAM_NUM_BMSK, soc_info);
 	mhi_cntrl->device_number = FIELD_GET(SOC_HW_VERSION_DEV_NUM_BMSK, soc_info);
diff --git a/include/linux/mhi.h b/include/linux/mhi.h
index f6de4b6..830df51 100644
--- a/include/linux/mhi.h
+++ b/include/linux/mhi.h
@@ -17,6 +17,20 @@
 
 #define MHI_MAX_OEM_PK_HASH_SEGMENTS 16
 
+/*
+ * List of workarounds for devices that require behavior not specified in
+ * the standard.
+ */
+enum mhi_quirks {
+	/*
+	 * Some devices do not properly initialize the SOC_HW_VERSION register
+	 * in the BHI space. In some instances, the value is 0xFFFFFFFF which
+	 * may hold special meaning. In the case of such devices, do not read
+	 * the register.
+	 */
+	MHI_QUIRK_SOC_HW_VERSION_UNRELIABLE		= BIT(0),
+};
+
 struct mhi_chan;
 struct mhi_event;
 struct mhi_ctxt;
@@ -273,6 +287,7 @@ struct mhi_event_config {
  * @event_cfg: Array of defined event rings
  * @use_bounce_buf: Use a bounce buffer pool due to limited DDR access
  * @m2_no_db: Host is not allowed to ring DB in M2 state
+ * @quirks: Workarounds for devices that require non-standard behavior
  */
 struct mhi_controller_config {
 	u32 max_channels;
@@ -284,6 +299,7 @@ struct mhi_controller_config {
 	struct mhi_event_config *event_cfg;
 	bool use_bounce_buf;
 	bool m2_no_db;
+	u32 quirks;
 };
 
 /**
@@ -358,6 +374,7 @@ struct mhi_controller_config {
  * @wake_set: Device wakeup set flag
  * @irq_flags: irq flags passed to request_irq (optional)
  * @mru: the default MRU for the MHI device
+ * @quirks: Workarounds for devices that require non-standard behavior
  *
  * Fields marked as (required) need to be populated by the controller driver
  * before calling mhi_register_controller(). For the fields marked as (optional)
@@ -452,6 +469,7 @@ struct mhi_controller {
 	bool wake_set;
 	unsigned long irq_flags;
 	u32 mru;
+	u32 quirks;
 };
 
 /**
-- 
2.7.4