accel/qaic: Implement quirk for SOC_HW_VERSION

[ Upstream commit 4c8874c2a6512b9fe7285cab1a6910d9211a6cfb ]

The SOC_HW_VERSION register in the BHI space is not correctly initialized
by the device and in many cases contains uninitialized data. The register
could contain 0xFFFFFFFF which is a special value to indicate a link
error in PCIe, therefore if observed, we could incorrectly think the
device is down.

Intercept reads for this register, and provide the correct value - every
production instance would read 0x60110200 if the device was operating as
intended.

Fixes: a36bf7af86 ("accel/qaic: Add MHI controller")
Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Reviewed-by: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@quicinc.com>
Reviewed-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231208163101.1295769-3-quic_jhugo@quicinc.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/accel/qaic/mhi_controller.c

@@ -404,8 +404,21 @@ static struct mhi_controller_config aic100_config = {
 
 static int mhi_read_reg(struct mhi_controller *mhi_cntrl, void __iomem *addr, u32 *out)
 {
-	u32 tmp = readl_relaxed(addr);
+	u32 tmp;
 
+	/*
+	 * SOC_HW_VERSION quirk
+	 * The SOC_HW_VERSION register (offset 0x224) is not reliable and
+	 * may contain uninitialized values, including 0xFFFFFFFF. This could
+	 * cause a false positive link down error.  Instead, intercept any
+	 * reads and provide the correct value of the register.
+	 */
+	if (addr - mhi_cntrl->regs == 0x224) {
+		*out = 0x60110200;
+		return 0;
+	}
+
+	tmp = readl_relaxed(addr);
 	if (tmp == U32_MAX)
 		return -EIO;