linux-kernel - Re: [PATCH] mthca: work around -Wenum-conversion warning

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Date:   Thu, 12 Nov 2020 11:57:09 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Arnd Bergmann <arnd@...nel.org>
CC:     Doug Ledford <dledford@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        <linux-rdma@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mthca: work around -Wenum-conversion warning

On Mon, Oct 26, 2020 at 10:12:30PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> gcc points out a suspicious mixing of enum types in a function that
> converts from MTHCA_OPCODE_* values to IB_WC_* values:
> 
> drivers/infiniband/hw/mthca/mthca_cq.c: In function 'mthca_poll_one':
> drivers/infiniband/hw/mthca/mthca_cq.c:607:21: warning: implicit conversion from 'enum <anonymous>' to 'enum ib_wc_opcode' [-Wenum-conversion]
>   607 |    entry->opcode    = MTHCA_OPCODE_INVALID;
> 
> Nothing seems to ever check for MTHCA_OPCODE_INVALID again, no
> idea if this is meaningful, but it seems harmless as it deals
> with an invalid input.
> 
> Add a cast to suppress the warning.
> 
> Fixes: 2a4443a69934 ("[PATCH] IB/mthca: fill in opcode field for send completions")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>  drivers/infiniband/hw/mthca/mthca_cq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/hw/mthca/mthca_cq.c b/drivers/infiniband/hw/mthca/mthca_cq.c
> index c3cfea243af8..319b8aa63f36 100644
> +++ b/drivers/infiniband/hw/mthca/mthca_cq.c
> @@ -604,7 +604,7 @@ static inline int mthca_poll_one(struct mthca_dev *dev,
>  			entry->byte_len  = MTHCA_ATOMIC_BYTE_LEN;
>  			break;
>  		default:
> -			entry->opcode    = MTHCA_OPCODE_INVALID;
> +			entry->opcode    = (u8)MTHCA_OPCODE_INVALID;
>  			break;

This code is completely bogus, sigh

Is this OK as far as the warning goes?

diff --git a/drivers/infiniband/hw/mthca/mthca_cq.c b/drivers/infiniband/hw/mthca/mthca_cq.c
index 319b8aa63f3645..36416f937b696c 100644
--- a/drivers/infiniband/hw/mthca/mthca_cq.c
+++ b/drivers/infiniband/hw/mthca/mthca_cq.c
@@ -604,7 +604,7 @@ static inline int mthca_poll_one(struct mthca_dev *dev,
 			entry->byte_len  = MTHCA_ATOMIC_BYTE_LEN;
 			break;
 		default:
-			entry->opcode    = (u8)MTHCA_OPCODE_INVALID;
+			entry->opcode = 0xFF;
 			break;
 		}
 	} else {
diff --git a/drivers/infiniband/hw/mthca/mthca_dev.h b/drivers/infiniband/hw/mthca/mthca_dev.h
index 9dbbf4d16796a4..a445160de3e16c 100644
--- a/drivers/infiniband/hw/mthca/mthca_dev.h
+++ b/drivers/infiniband/hw/mthca/mthca_dev.h
@@ -105,7 +105,6 @@ enum {
 	MTHCA_OPCODE_ATOMIC_CS      = 0x11,
 	MTHCA_OPCODE_ATOMIC_FA      = 0x12,
 	MTHCA_OPCODE_BIND_MW        = 0x18,
-	MTHCA_OPCODE_INVALID        = 0xff
 };
 
 enum {