[PATCH] scsi: dc395x: correctly discard the return value in certain reads

[PATCH] scsi: dc395x: correctly discard the return value in certain reads

[Xinhui Yang]

There are certain read operations performed in this code which doesn't
really don't need its return value. Those read operations either clears
the FIFO buffer, or clears the interruption status. However, unused read
triggers compiler warnings. With CONFIG_WERROR on, these warnings get
converted into errors:

drivers/scsi/dc395x.c: In function ‘__dc395x_eh_bus_reset’:
drivers/scsi/dc395x.c:97:49: error: value computed is not used [-Werror=unused-value]
   97 | #define DC395x_read8(acb,address)               (u8)(inb(acb->io_port_base + (address)))
      |                                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/dc395x.c:1003:9: note: in expansion of macro ‘DC395x_read8’
 1003 |         DC395x_read8(acb, TRM_S1040_SCSI_INTSTATUS);
      |         ^~~~~~~~~~~~
drivers/scsi/dc395x.c: In function ‘data_io_transfer’:
drivers/scsi/dc395x.c:97:49: error: value computed is not used [-Werror=unused-value]
   97 | #define DC395x_read8(acb,address)               (u8)(inb(acb->io_port_base + (address)))
      |                                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/dc395x.c:2032:33: note: in expansion of macro ‘DC395x_read8’
 2032 |                                 DC395x_read8(acb, TRM_S1040_SCSI_FIFO);

Create a new macro DC395x_peek8() to deliberately cast the return value
to void, which tells the compiler we really don't need the return value
of such read operations.

Signed-off-by: Xinhui Yang <cyan@cyano.uk>
---
 drivers/scsi/dc395x.c | 34 ++++++++++++++++++++--------------
 1 file changed, 20 insertions(+), 14 deletions(-)

diff --git a/drivers/scsi/dc395x.c b/drivers/scsi/dc395x.c
index 386c8359e1cc..013d0d5277d6 100644
--- a/drivers/scsi/dc395x.c
+++ b/drivers/scsi/dc395x.c
@@ -91,15 +91,21 @@
 #endif
 
 
-#define DC395x_LOCK_IO(dev,flags)		spin_lock_irqsave(((struct Scsi_Host *)dev)->host_lock, flags)
-#define DC395x_UNLOCK_IO(dev,flags)		spin_unlock_irqrestore(((struct Scsi_Host *)dev)->host_lock, flags)
+#define DC395x_LOCK_IO(dev, flags)		spin_lock_irqsave(((struct Scsi_Host *)dev)->host_lock, flags)
+#define DC395x_UNLOCK_IO(dev, flags)		spin_unlock_irqrestore(((struct Scsi_Host *)dev)->host_lock, flags)
 
-#define DC395x_read8(acb,address)		(u8)(inb(acb->io_port_base + (address)))
-#define DC395x_read16(acb,address)		(u16)(inw(acb->io_port_base + (address)))
-#define DC395x_read32(acb,address)		(u32)(inl(acb->io_port_base + (address)))
-#define DC395x_write8(acb,address,value)	outb((value), acb->io_port_base + (address))
-#define DC395x_write16(acb,address,value)	outw((value), acb->io_port_base + (address))
-#define DC395x_write32(acb,address,value)	outl((value), acb->io_port_base + (address))
+/*
+ * read operations that may trigger side effects in the hardware,
+ * but the value can or should be discarded.
+ */
+#define DC395x_peek8(acb, address)		((void)(inb(acb->io_port_base + (address))))
+/* Normal read write operations goes here. */
+#define DC395x_read8(acb, address)		((u8)    (inb(acb->io_port_base + (address))))
+#define DC395x_read16(acb, address)		((u16)   (inw(acb->io_port_base + (address))))
+#define DC395x_read32(acb, address)		((u32)   (inl(acb->io_port_base + (address))))
+#define DC395x_write8(acb, address, value)	(outb((value), acb->io_port_base + (address)))
+#define DC395x_write16(acb, address, value)	(outw((value), acb->io_port_base + (address)))
+#define DC395x_write32(acb, address, value)	(outl((value), acb->io_port_base + (address)))
 
 #define TAG_NONE 255
 
@@ -1000,7 +1006,7 @@ static int __dc395x_eh_bus_reset(struct scsi_cmnd *cmd)
 	DC395x_write8(acb, TRM_S1040_DMA_CONTROL, CLRXFIFO);
 	clear_fifo(acb, "eh_bus_reset");
 	/* Delete pending IRQ */
-	DC395x_read8(acb, TRM_S1040_SCSI_INTSTATUS);
+	DC395x_peek8(acb, TRM_S1040_SCSI_INTSTATUS);
 	set_basic_config(acb);
 
 	reset_dev_param(acb);
@@ -2029,8 +2035,8 @@ static void data_io_transfer(struct AdapterCtlBlk *acb,
 			DC395x_write8(acb, TRM_S1040_SCSI_CONFIG2,
 				      CFG2_WIDEFIFO);
 			if (io_dir & DMACMD_DIR) {
-				DC395x_read8(acb, TRM_S1040_SCSI_FIFO);
-				DC395x_read8(acb, TRM_S1040_SCSI_FIFO);
+				DC395x_peek8(acb, TRM_S1040_SCSI_FIFO);
+				DC395x_peek8(acb, TRM_S1040_SCSI_FIFO);
 			} else {
 				/* Danger, Robinson: If you find KGs
 				 * scattered over the wide disk, the driver
@@ -2044,7 +2050,7 @@ static void data_io_transfer(struct AdapterCtlBlk *acb,
 			/* Danger, Robinson: If you find a collection of Ks on your disk
 			 * something broke :-( */
 			if (io_dir & DMACMD_DIR)
-				DC395x_read8(acb, TRM_S1040_SCSI_FIFO);
+				DC395x_peek8(acb, TRM_S1040_SCSI_FIFO);
 			else
 				DC395x_write8(acb, TRM_S1040_SCSI_FIFO, 'K');
 		}
@@ -2892,7 +2898,7 @@ static void set_basic_config(struct AdapterCtlBlk *acb)
 	    DMA_FIFO_HALF_HALF | DMA_ENHANCE /*| DMA_MEM_MULTI_READ */ ;
 	DC395x_write16(acb, TRM_S1040_DMA_CONFIG, wval);
 	/* Clear pending interrupt status */
-	DC395x_read8(acb, TRM_S1040_SCSI_INTSTATUS);
+	DC395x_peek8(acb, TRM_S1040_SCSI_INTSTATUS);
 	/* Enable SCSI interrupt    */
 	DC395x_write8(acb, TRM_S1040_SCSI_INTEN, 0x7F);
 	DC395x_write8(acb, TRM_S1040_DMA_INTEN, EN_SCSIINTR | EN_DMAXFERERROR
@@ -3799,7 +3805,7 @@ static void adapter_uninit_chip(struct AdapterCtlBlk *acb)
 		reset_scsi_bus(acb);
 
 	/* clear any pending interrupt state */
-	DC395x_read8(acb, TRM_S1040_SCSI_INTSTATUS);
+	DC395x_peek8(acb, TRM_S1040_SCSI_INTSTATUS);
 }
 
 
-- 
2.51.0

Re: [PATCH] scsi: dc395x: correctly discard the return value in certain reads

[kernel test robot]

Hi,

Thanks for your patch.

FYI: kernel test robot notices the stable kernel rule is not satisfied.

The check is based on https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#option-1

Rule: add the tag "Cc: stable@vger.kernel.org" in the sign-off area to have the patch automatically included in the stable tree.
Subject: [PATCH] scsi: dc395x: correctly discard the return value in certain reads
Link: https://lore.kernel.org/stable/20250922143619.824129-1-cyan%40cyano.uk

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