* [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-03-23 13:15 ` Arnd Bergmann
0 siblings, 0 replies; 13+ messages in thread
From: Arnd Bergmann @ 2021-03-23 13:15 UTC (permalink / raw)
To: Li Yang, Roy Pledge, Claudiu Manoil, Scott Wood
Cc: soc, Arnd Bergmann, Jakub Kicinski, Lee Jones,
Sebastian Andrzej Siewior, YueHaibing, linuxppc-dev,
linux-arm-kernel, linux-kernel
From: Arnd Bergmann <arnd@arndb.de>
When building with W=1, gcc points out that the __packed attribute
on struct qm_eqcr_entry conflicts with the 8-byte alignment
attribute on struct qm_fd inside it:
drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
I assume that the alignment attribute is the correct one, and
that qm_eqcr_entry cannot actually be unaligned in memory,
so add the same alignment on the outer struct.
Fixes: c535e923bb97 ("soc/fsl: Introduce DPAA 1.x QMan device driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
drivers/soc/fsl/qbman/qman.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
index a1b9be1d105a..fde4edd83c14 100644
--- a/drivers/soc/fsl/qbman/qman.c
+++ b/drivers/soc/fsl/qbman/qman.c
@@ -186,7 +186,7 @@ struct qm_eqcr_entry {
__be32 tag;
struct qm_fd fd;
u8 __reserved3[32];
-} __packed;
+} __packed __aligned(8);
#define QM_EQCR_VERB_VBIT 0x80
#define QM_EQCR_VERB_CMD_MASK 0x61 /* but only one value; */
#define QM_EQCR_VERB_CMD_ENQUEUE 0x01
--
2.29.2
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-03-23 13:15 ` Arnd Bergmann
0 siblings, 0 replies; 13+ messages in thread
From: Arnd Bergmann @ 2021-03-23 13:15 UTC (permalink / raw)
To: Li Yang, Roy Pledge, Claudiu Manoil, Scott Wood
Cc: Arnd Bergmann, linuxppc-dev, Sebastian Andrzej Siewior,
YueHaibing, linux-kernel, soc, Jakub Kicinski, Lee Jones,
linux-arm-kernel
From: Arnd Bergmann <arnd@arndb.de>
When building with W=1, gcc points out that the __packed attribute
on struct qm_eqcr_entry conflicts with the 8-byte alignment
attribute on struct qm_fd inside it:
drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
I assume that the alignment attribute is the correct one, and
that qm_eqcr_entry cannot actually be unaligned in memory,
so add the same alignment on the outer struct.
Fixes: c535e923bb97 ("soc/fsl: Introduce DPAA 1.x QMan device driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
drivers/soc/fsl/qbman/qman.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
index a1b9be1d105a..fde4edd83c14 100644
--- a/drivers/soc/fsl/qbman/qman.c
+++ b/drivers/soc/fsl/qbman/qman.c
@@ -186,7 +186,7 @@ struct qm_eqcr_entry {
__be32 tag;
struct qm_fd fd;
u8 __reserved3[32];
-} __packed;
+} __packed __aligned(8);
#define QM_EQCR_VERB_VBIT 0x80
#define QM_EQCR_VERB_CMD_MASK 0x61 /* but only one value; */
#define QM_EQCR_VERB_CMD_ENQUEUE 0x01
--
2.29.2
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-03-23 13:15 ` Arnd Bergmann
0 siblings, 0 replies; 13+ messages in thread
From: Arnd Bergmann @ 2021-03-23 13:15 UTC (permalink / raw)
To: Li Yang, Roy Pledge, Claudiu Manoil, Scott Wood
Cc: soc, Arnd Bergmann, Jakub Kicinski, Lee Jones,
Sebastian Andrzej Siewior, YueHaibing, linuxppc-dev,
linux-arm-kernel, linux-kernel
From: Arnd Bergmann <arnd@arndb.de>
When building with W=1, gcc points out that the __packed attribute
on struct qm_eqcr_entry conflicts with the 8-byte alignment
attribute on struct qm_fd inside it:
drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
I assume that the alignment attribute is the correct one, and
that qm_eqcr_entry cannot actually be unaligned in memory,
so add the same alignment on the outer struct.
Fixes: c535e923bb97 ("soc/fsl: Introduce DPAA 1.x QMan device driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
drivers/soc/fsl/qbman/qman.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
index a1b9be1d105a..fde4edd83c14 100644
--- a/drivers/soc/fsl/qbman/qman.c
+++ b/drivers/soc/fsl/qbman/qman.c
@@ -186,7 +186,7 @@ struct qm_eqcr_entry {
__be32 tag;
struct qm_fd fd;
u8 __reserved3[32];
-} __packed;
+} __packed __aligned(8);
#define QM_EQCR_VERB_VBIT 0x80
#define QM_EQCR_VERB_CMD_MASK 0x61 /* but only one value; */
#define QM_EQCR_VERB_CMD_ENQUEUE 0x01
--
2.29.2
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
2021-03-23 13:15 ` Arnd Bergmann
(?)
(?)
@ 2021-03-26 2:17 ` Li Yang
-1 siblings, 0 replies; 13+ messages in thread
From: Li Yang @ 2021-03-26 2:17 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Roy Pledge, Claudiu Manoil, Scott Wood, Arnd Bergmann,
linuxppc-dev, Sebastian Andrzej Siewior, YueHaibing, lkml, soc,
Jakub Kicinski, Lee Jones,
moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE,
Madalin-cristian Bucur
On Tue, Mar 23, 2021 at 8:17 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> When building with W=1, gcc points out that the __packed attribute
> on struct qm_eqcr_entry conflicts with the 8-byte alignment
> attribute on struct qm_fd inside it:
>
> drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
>
> I assume that the alignment attribute is the correct one, and
> that qm_eqcr_entry cannot actually be unaligned in memory,
> so add the same alignment on the outer struct.
>
> Fixes: c535e923bb97 ("soc/fsl: Introduce DPAA 1.x QMan device driver")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> drivers/soc/fsl/qbman/qman.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
> index a1b9be1d105a..fde4edd83c14 100644
> --- a/drivers/soc/fsl/qbman/qman.c
> +++ b/drivers/soc/fsl/qbman/qman.c
> @@ -186,7 +186,7 @@ struct qm_eqcr_entry {
> __be32 tag;
> struct qm_fd fd;
> u8 __reserved3[32];
> -} __packed;
> +} __packed __aligned(8);
The EQCR structure is actually aligned on 64-byte from the manual.
But probably 8 is enough to let the compiler not complain.
> #define QM_EQCR_VERB_VBIT 0x80
> #define QM_EQCR_VERB_CMD_MASK 0x61 /* but only one value; */
> #define QM_EQCR_VERB_CMD_ENQUEUE 0x01
> --
> 2.29.2
>
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-03-26 2:17 ` Li Yang
0 siblings, 0 replies; 13+ messages in thread
From: Li Yang @ 2021-03-26 2:17 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Roy Pledge, Claudiu Manoil, Scott Wood, Arnd Bergmann,
linuxppc-dev, Sebastian Andrzej Siewior, YueHaibing, lkml, soc,
Jakub Kicinski, Lee Jones,
moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE,
Madalin-cristian Bucur
On Tue, Mar 23, 2021 at 8:17 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> When building with W=1, gcc points out that the __packed attribute
> on struct qm_eqcr_entry conflicts with the 8-byte alignment
> attribute on struct qm_fd inside it:
>
> drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
>
> I assume that the alignment attribute is the correct one, and
> that qm_eqcr_entry cannot actually be unaligned in memory,
> so add the same alignment on the outer struct.
>
> Fixes: c535e923bb97 ("soc/fsl: Introduce DPAA 1.x QMan device driver")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> drivers/soc/fsl/qbman/qman.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
> index a1b9be1d105a..fde4edd83c14 100644
> --- a/drivers/soc/fsl/qbman/qman.c
> +++ b/drivers/soc/fsl/qbman/qman.c
> @@ -186,7 +186,7 @@ struct qm_eqcr_entry {
> __be32 tag;
> struct qm_fd fd;
> u8 __reserved3[32];
> -} __packed;
> +} __packed __aligned(8);
The EQCR structure is actually aligned on 64-byte from the manual.
But probably 8 is enough to let the compiler not complain.
> #define QM_EQCR_VERB_VBIT 0x80
> #define QM_EQCR_VERB_CMD_MASK 0x61 /* but only one value; */
> #define QM_EQCR_VERB_CMD_ENQUEUE 0x01
> --
> 2.29.2
>
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-03-26 2:17 ` Li Yang
0 siblings, 0 replies; 13+ messages in thread
From: Li Yang @ 2021-03-26 2:17 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Arnd Bergmann, Madalin-cristian Bucur, soc, Lee Jones,
Roy Pledge, YueHaibing, lkml, Scott Wood, Claudiu Manoil,
Jakub Kicinski, linuxppc-dev, Sebastian Andrzej Siewior,
moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE
On Tue, Mar 23, 2021 at 8:17 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> When building with W=1, gcc points out that the __packed attribute
> on struct qm_eqcr_entry conflicts with the 8-byte alignment
> attribute on struct qm_fd inside it:
>
> drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
>
> I assume that the alignment attribute is the correct one, and
> that qm_eqcr_entry cannot actually be unaligned in memory,
> so add the same alignment on the outer struct.
>
> Fixes: c535e923bb97 ("soc/fsl: Introduce DPAA 1.x QMan device driver")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> drivers/soc/fsl/qbman/qman.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
> index a1b9be1d105a..fde4edd83c14 100644
> --- a/drivers/soc/fsl/qbman/qman.c
> +++ b/drivers/soc/fsl/qbman/qman.c
> @@ -186,7 +186,7 @@ struct qm_eqcr_entry {
> __be32 tag;
> struct qm_fd fd;
> u8 __reserved3[32];
> -} __packed;
> +} __packed __aligned(8);
The EQCR structure is actually aligned on 64-byte from the manual.
But probably 8 is enough to let the compiler not complain.
> #define QM_EQCR_VERB_VBIT 0x80
> #define QM_EQCR_VERB_CMD_MASK 0x61 /* but only one value; */
> #define QM_EQCR_VERB_CMD_ENQUEUE 0x01
> --
> 2.29.2
>
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-03-26 2:17 ` Li Yang
0 siblings, 0 replies; 13+ messages in thread
From: Li Yang @ 2021-03-26 2:17 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Roy Pledge, Claudiu Manoil, Scott Wood, Arnd Bergmann,
linuxppc-dev, Sebastian Andrzej Siewior, YueHaibing, lkml, soc,
Jakub Kicinski, Lee Jones,
moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE,
Madalin-cristian Bucur
On Tue, Mar 23, 2021 at 8:17 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> When building with W=1, gcc points out that the __packed attribute
> on struct qm_eqcr_entry conflicts with the 8-byte alignment
> attribute on struct qm_fd inside it:
>
> drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
>
> I assume that the alignment attribute is the correct one, and
> that qm_eqcr_entry cannot actually be unaligned in memory,
> so add the same alignment on the outer struct.
>
> Fixes: c535e923bb97 ("soc/fsl: Introduce DPAA 1.x QMan device driver")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> drivers/soc/fsl/qbman/qman.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
> index a1b9be1d105a..fde4edd83c14 100644
> --- a/drivers/soc/fsl/qbman/qman.c
> +++ b/drivers/soc/fsl/qbman/qman.c
> @@ -186,7 +186,7 @@ struct qm_eqcr_entry {
> __be32 tag;
> struct qm_fd fd;
> u8 __reserved3[32];
> -} __packed;
> +} __packed __aligned(8);
The EQCR structure is actually aligned on 64-byte from the manual.
But probably 8 is enough to let the compiler not complain.
> #define QM_EQCR_VERB_VBIT 0x80
> #define QM_EQCR_VERB_CMD_MASK 0x61 /* but only one value; */
> #define QM_EQCR_VERB_CMD_ENQUEUE 0x01
> --
> 2.29.2
>
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-03-26 8:51 ` Arnd Bergmann
0 siblings, 0 replies; 13+ messages in thread
From: Arnd Bergmann @ 2021-03-26 8:51 UTC (permalink / raw)
To: Li Yang
Cc: Roy Pledge, Claudiu Manoil, Scott Wood, linuxppc-dev,
Sebastian Andrzej Siewior, YueHaibing, lkml, SoC Team,
Jakub Kicinski, Lee Jones,
moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE,
Madalin-cristian Bucur
On Fri, Mar 26, 2021 at 3:17 AM Li Yang <leoyang.li@nxp.com> wrote:
> On Tue, Mar 23, 2021 at 8:17 AM Arnd Bergmann <arnd@kernel.org> wrote:
> >
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > When building with W=1, gcc points out that the __packed attribute
> > on struct qm_eqcr_entry conflicts with the 8-byte alignment
> > attribute on struct qm_fd inside it:
> >
> > drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
> >
> > I assume that the alignment attribute is the correct one, and
> > that qm_eqcr_entry cannot actually be unaligned in memory,
> > so add the same alignment on the outer struct.
> >
> > Fixes: c535e923bb97 ("soc/fsl: Introduce DPAA 1.x QMan device driver")
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> > drivers/soc/fsl/qbman/qman.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
> > index a1b9be1d105a..fde4edd83c14 100644
> > --- a/drivers/soc/fsl/qbman/qman.c
> > +++ b/drivers/soc/fsl/qbman/qman.c
> > @@ -186,7 +186,7 @@ struct qm_eqcr_entry {
> > __be32 tag;
> > struct qm_fd fd;
> > u8 __reserved3[32];
> > -} __packed;
> > +} __packed __aligned(8);
>
> The EQCR structure is actually aligned on 64-byte from the manual.
> But probably 8 is enough to let the compiler not complain.
The important bit is that all members inside are at most 8-byte long
and naturally aligned, so the compiler can now optimize the accesses
because it can assume that each member can be updated atomically.
Marking a structure as unaligned with the __packed attribute can lead
to rather unoptimized code, which is particularly important when the
structure is mapped as uncached -- accessing it one byte at a time
means you have eight times the latency for a simple read. I think on
arm64, the compiler doesn't actually have to do that, but at least if you
run a 32-bit kernel, the packing would prevent the use of ldrd or ldm
instructions that need an aligned word.
Arnd
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-03-26 8:51 ` Arnd Bergmann
0 siblings, 0 replies; 13+ messages in thread
From: Arnd Bergmann @ 2021-03-26 8:51 UTC (permalink / raw)
To: Li Yang
Cc: Madalin-cristian Bucur, SoC Team, Lee Jones, Roy Pledge,
YueHaibing, lkml, Scott Wood, Claudiu Manoil, Jakub Kicinski,
linuxppc-dev, Sebastian Andrzej Siewior,
moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE
On Fri, Mar 26, 2021 at 3:17 AM Li Yang <leoyang.li@nxp.com> wrote:
> On Tue, Mar 23, 2021 at 8:17 AM Arnd Bergmann <arnd@kernel.org> wrote:
> >
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > When building with W=1, gcc points out that the __packed attribute
> > on struct qm_eqcr_entry conflicts with the 8-byte alignment
> > attribute on struct qm_fd inside it:
> >
> > drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
> >
> > I assume that the alignment attribute is the correct one, and
> > that qm_eqcr_entry cannot actually be unaligned in memory,
> > so add the same alignment on the outer struct.
> >
> > Fixes: c535e923bb97 ("soc/fsl: Introduce DPAA 1.x QMan device driver")
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> > drivers/soc/fsl/qbman/qman.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
> > index a1b9be1d105a..fde4edd83c14 100644
> > --- a/drivers/soc/fsl/qbman/qman.c
> > +++ b/drivers/soc/fsl/qbman/qman.c
> > @@ -186,7 +186,7 @@ struct qm_eqcr_entry {
> > __be32 tag;
> > struct qm_fd fd;
> > u8 __reserved3[32];
> > -} __packed;
> > +} __packed __aligned(8);
>
> The EQCR structure is actually aligned on 64-byte from the manual.
> But probably 8 is enough to let the compiler not complain.
The important bit is that all members inside are at most 8-byte long
and naturally aligned, so the compiler can now optimize the accesses
because it can assume that each member can be updated atomically.
Marking a structure as unaligned with the __packed attribute can lead
to rather unoptimized code, which is particularly important when the
structure is mapped as uncached -- accessing it one byte at a time
means you have eight times the latency for a simple read. I think on
arm64, the compiler doesn't actually have to do that, but at least if you
run a 32-bit kernel, the packing would prevent the use of ldrd or ldm
instructions that need an aligned word.
Arnd
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-03-26 8:51 ` Arnd Bergmann
0 siblings, 0 replies; 13+ messages in thread
From: Arnd Bergmann @ 2021-03-26 8:51 UTC (permalink / raw)
To: Li Yang
Cc: Roy Pledge, Claudiu Manoil, Scott Wood, linuxppc-dev,
Sebastian Andrzej Siewior, YueHaibing, lkml, SoC Team,
Jakub Kicinski, Lee Jones,
moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE,
Madalin-cristian Bucur
On Fri, Mar 26, 2021 at 3:17 AM Li Yang <leoyang.li@nxp.com> wrote:
> On Tue, Mar 23, 2021 at 8:17 AM Arnd Bergmann <arnd@kernel.org> wrote:
> >
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > When building with W=1, gcc points out that the __packed attribute
> > on struct qm_eqcr_entry conflicts with the 8-byte alignment
> > attribute on struct qm_fd inside it:
> >
> > drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
> >
> > I assume that the alignment attribute is the correct one, and
> > that qm_eqcr_entry cannot actually be unaligned in memory,
> > so add the same alignment on the outer struct.
> >
> > Fixes: c535e923bb97 ("soc/fsl: Introduce DPAA 1.x QMan device driver")
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> > drivers/soc/fsl/qbman/qman.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
> > index a1b9be1d105a..fde4edd83c14 100644
> > --- a/drivers/soc/fsl/qbman/qman.c
> > +++ b/drivers/soc/fsl/qbman/qman.c
> > @@ -186,7 +186,7 @@ struct qm_eqcr_entry {
> > __be32 tag;
> > struct qm_fd fd;
> > u8 __reserved3[32];
> > -} __packed;
> > +} __packed __aligned(8);
>
> The EQCR structure is actually aligned on 64-byte from the manual.
> But probably 8 is enough to let the compiler not complain.
The important bit is that all members inside are at most 8-byte long
and naturally aligned, so the compiler can now optimize the accesses
because it can assume that each member can be updated atomically.
Marking a structure as unaligned with the __packed attribute can lead
to rather unoptimized code, which is particularly important when the
structure is mapped as uncached -- accessing it one byte at a time
means you have eight times the latency for a simple read. I think on
arm64, the compiler doesn't actually have to do that, but at least if you
run a 32-bit kernel, the packing would prevent the use of ldrd or ldm
instructions that need an aligned word.
Arnd
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
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^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-04-01 10:23 ` Arnd Bergmann
0 siblings, 0 replies; 13+ messages in thread
From: Arnd Bergmann @ 2021-04-01 10:23 UTC (permalink / raw)
To: Roy Pledge, Claudiu Manoil, Scott Wood, Arnd Bergmann, Li Yang
Cc: Arnd Bergmann, linux-kernel, linux-arm-kernel, Lee Jones, soc,
Sebastian Andrzej Siewior, Jakub Kicinski, YueHaibing,
linuxppc-dev
From: Arnd Bergmann <arnd@arndb.de>
On Tue, 23 Mar 2021 14:15:23 +0100, Arnd Bergmann wrote:
> When building with W=1, gcc points out that the __packed attribute
> on struct qm_eqcr_entry conflicts with the 8-byte alignment
> attribute on struct qm_fd inside it:
>
> drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
>
> I assume that the alignment attribute is the correct one, and
> that qm_eqcr_entry cannot actually be unaligned in memory,
> so add the same alignment on the outer struct.
Applied to arm/fixes
[1/1] soc/fsl: qbman: fix conflicting alignment attributes
commit: b9ab2619047edc1c6c07dc68963d84a5979f0abe
Arnd
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-04-01 10:23 ` Arnd Bergmann
0 siblings, 0 replies; 13+ messages in thread
From: Arnd Bergmann @ 2021-04-01 10:23 UTC (permalink / raw)
To: Roy Pledge, Claudiu Manoil, Scott Wood, Arnd Bergmann, Li Yang
Cc: Arnd Bergmann, linuxppc-dev, Sebastian Andrzej Siewior,
YueHaibing, linux-kernel, soc, Jakub Kicinski, Lee Jones,
linux-arm-kernel
From: Arnd Bergmann <arnd@arndb.de>
On Tue, 23 Mar 2021 14:15:23 +0100, Arnd Bergmann wrote:
> When building with W=1, gcc points out that the __packed attribute
> on struct qm_eqcr_entry conflicts with the 8-byte alignment
> attribute on struct qm_fd inside it:
>
> drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
>
> I assume that the alignment attribute is the correct one, and
> that qm_eqcr_entry cannot actually be unaligned in memory,
> so add the same alignment on the outer struct.
Applied to arm/fixes
[1/1] soc/fsl: qbman: fix conflicting alignment attributes
commit: b9ab2619047edc1c6c07dc68963d84a5979f0abe
Arnd
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH] soc/fsl: qbman: fix conflicting alignment attributes
@ 2021-04-01 10:23 ` Arnd Bergmann
0 siblings, 0 replies; 13+ messages in thread
From: Arnd Bergmann @ 2021-04-01 10:23 UTC (permalink / raw)
To: Roy Pledge, Claudiu Manoil, Scott Wood, Arnd Bergmann, Li Yang
Cc: Arnd Bergmann, linux-kernel, linux-arm-kernel, Lee Jones, soc,
Sebastian Andrzej Siewior, Jakub Kicinski, YueHaibing,
linuxppc-dev
From: Arnd Bergmann <arnd@arndb.de>
On Tue, 23 Mar 2021 14:15:23 +0100, Arnd Bergmann wrote:
> When building with W=1, gcc points out that the __packed attribute
> on struct qm_eqcr_entry conflicts with the 8-byte alignment
> attribute on struct qm_fd inside it:
>
> drivers/soc/fsl/qbman/qman.c:189:1: error: alignment 1 of 'struct qm_eqcr_entry' is less than 8 [-Werror=packed-not-aligned]
>
> I assume that the alignment attribute is the correct one, and
> that qm_eqcr_entry cannot actually be unaligned in memory,
> so add the same alignment on the outer struct.
Applied to arm/fixes
[1/1] soc/fsl: qbman: fix conflicting alignment attributes
commit: b9ab2619047edc1c6c07dc68963d84a5979f0abe
Arnd
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^ permalink raw reply [flat|nested] 13+ messages in thread
end of thread, other threads:[~2021-04-01 10:26 UTC | newest]
Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-03-23 13:15 [PATCH] soc/fsl: qbman: fix conflicting alignment attributes Arnd Bergmann
2021-03-23 13:15 ` Arnd Bergmann
2021-03-23 13:15 ` Arnd Bergmann
2021-03-26 2:17 ` Li Yang
2021-03-26 2:17 ` Li Yang
2021-03-26 2:17 ` Li Yang
2021-03-26 2:17 ` Li Yang
2021-03-26 8:51 ` Arnd Bergmann
2021-03-26 8:51 ` Arnd Bergmann
2021-03-26 8:51 ` Arnd Bergmann
2021-04-01 10:23 ` Arnd Bergmann
2021-04-01 10:23 ` Arnd Bergmann
2021-04-01 10:23 ` Arnd Bergmann
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