bus: mhi: core: Ensure non-zero session or sequence ID values are used

While writing any sequence or session identifiers, it is possible that
the host could write a zero value, whereas only non-zero values should
be supported writes to those registers. Ensure that the host does not
write a non-zero value for them and also log them in debug messages. A
macro is introduced to simplify this check and the existing checks are
also converted to use this macro.

Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20200521170249.21795-9-manivannan.sadhasivam@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/bus/mhi/core/boot.c

@@ -43,10 +43,7 @@ void mhi_rddm_prepare(struct mhi_controller *mhi_cntrl,
 		      lower_32_bits(mhi_buf->dma_addr));
 
 	mhi_write_reg(mhi_cntrl, base, BHIE_RXVECSIZE_OFFS, mhi_buf->len);
-	sequence_id = prandom_u32() & BHIE_RXVECSTATUS_SEQNUM_BMSK;
-
-	if (unlikely(!sequence_id))
-		sequence_id = 1;
+	sequence_id = MHI_RANDOM_U32_NONZERO(BHIE_RXVECSTATUS_SEQNUM_BMSK);
 
 	mhi_write_reg_field(mhi_cntrl, base, BHIE_RXVECDB_OFFS,
 			    BHIE_RXVECDB_SEQNUM_BMSK, BHIE_RXVECDB_SEQNUM_SHFT,
@@ -189,7 +186,9 @@ static int mhi_fw_load_amss(struct mhi_controller *mhi_cntrl,
 		return -EIO;
 	}
 
-	dev_dbg(dev, "Starting AMSS download via BHIe\n");
+	sequence_id = MHI_RANDOM_U32_NONZERO(BHIE_TXVECSTATUS_SEQNUM_BMSK);
+	dev_dbg(dev, "Starting AMSS download via BHIe. Sequence ID:%u\n",
+		sequence_id);
 	mhi_write_reg(mhi_cntrl, base, BHIE_TXVECADDR_HIGH_OFFS,
 		      upper_32_bits(mhi_buf->dma_addr));
 
@@ -198,7 +197,6 @@ static int mhi_fw_load_amss(struct mhi_controller *mhi_cntrl,
 
 	mhi_write_reg(mhi_cntrl, base, BHIE_TXVECSIZE_OFFS, mhi_buf->len);
 
-	sequence_id = prandom_u32() & BHIE_TXVECSTATUS_SEQNUM_BMSK;
 	mhi_write_reg_field(mhi_cntrl, base, BHIE_TXVECDB_OFFS,
 			    BHIE_TXVECDB_SEQNUM_BMSK, BHIE_TXVECDB_SEQNUM_SHFT,
 			    sequence_id);
@@ -246,14 +244,15 @@ static int mhi_fw_load_sbl(struct mhi_controller *mhi_cntrl,
 		goto invalid_pm_state;
 	}
 
-	dev_dbg(dev, "Starting SBL download via BHI\n");
+	session_id = MHI_RANDOM_U32_NONZERO(BHI_TXDB_SEQNUM_BMSK);
+	dev_dbg(dev, "Starting SBL download via BHI. Session ID:%u\n",
+		session_id);
 	mhi_write_reg(mhi_cntrl, base, BHI_STATUS, 0);
 	mhi_write_reg(mhi_cntrl, base, BHI_IMGADDR_HIGH,
 		      upper_32_bits(dma_addr));
 	mhi_write_reg(mhi_cntrl, base, BHI_IMGADDR_LOW,
 		      lower_32_bits(dma_addr));
 	mhi_write_reg(mhi_cntrl, base, BHI_IMGSIZE, size);
-	session_id = prandom_u32() & BHI_TXDB_SEQNUM_BMSK;
 	mhi_write_reg(mhi_cntrl, base, BHI_IMGTXDB, session_id);
 	read_unlock_bh(pm_lock);
 

drivers/bus/mhi/core/internal.h

@@ -452,6 +452,7 @@ enum mhi_pm_state {
 #define PRIMARY_CMD_RING		0
 #define MHI_DEV_WAKE_DB			127
 #define MHI_MAX_MTU			0xffff
+#define MHI_RANDOM_U32_NONZERO(bmsk)	(prandom_u32_max(bmsk) + 1)
 
 enum mhi_er_type {
 	MHI_ER_TYPE_INVALID = 0x0,