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(-)
On Tue, Mar 23, 2021 at 8:17 AM Arnd Bergmann [off-list ref] wrote:
quoted hunk
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(-)
On Fri, Mar 26, 2021 at 3:17 AM Li Yang [off-list ref] wrote:
On Tue, Mar 23, 2021 at 8:17 AM Arnd Bergmann [off-list ref] wrote:
quoted
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(-)
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
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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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