On 3/20/2018 9:54 AM, Jason Gunthorpe wrote:
> On Mon, Mar 19, 2018 at 10:47:47PM -0400, Sinan Kaya wrote:
>> Code includes barrier() followed by writel(). writel() already has a
>> barrier on some architectures like arm64.
>>
>> This ends up CPU observing two barriers back to back before executing the
>> register write.
>>
>> Create a new wrapper function with relaxed write operator. Use the new
>> wrapper when a write is following a barrier().
>>
>> Signed-off-by: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
>> drivers/infiniband/hw/nes/nes.h | 5 +++++
>> drivers/infiniband/hw/nes/nes_hw.c | 21 ++++++++++++++-------
>> drivers/infiniband/hw/nes/nes_mgt.c | 15 ++++++++++-----
>> drivers/infiniband/hw/nes/nes_nic.c | 2 +-
>> drivers/infiniband/hw/nes/nes_utils.c | 3 ++-
>> drivers/infiniband/hw/nes/nes_verbs.c | 5 +++--
>> 6 files changed, 35 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/infiniband/hw/nes/nes.h b/drivers/infiniband/hw/nes/nes.h
>> index 00c27291..85e007d 100644
>> +++ b/drivers/infiniband/hw/nes/nes.h
>> @@ -387,6 +387,11 @@ static inline void nes_write_indexed(struct nes_device *nesdev, u32 reg_index, u
>> spin_unlock_irqrestore(&nesdev->indexed_regs_lock, flags);
>> }
>>
>> +static inline void nes_write32_relaxed(void __iomem *addr, u32 val)
>> +{
>> + writel_relaxed(val, addr);
>> +}
>
> This wrapper is pointless, let us not add more..
>
>> static inline void nes_write32(void __iomem *addr, u32 val)
>> {
>> writel(val, addr);
>> diff --git a/drivers/infiniband/hw/nes/nes_hw.c b/drivers/infiniband/hw/nes/nes_hw.c
>> index 18a7de1..568e17d 100644
>> +++ b/drivers/infiniband/hw/nes/nes_hw.c
>> @@ -1257,7 +1257,8 @@ int nes_destroy_cqp(struct nes_device *nesdev)
>>
>> barrier();
>> /* Ring doorbell (5 WQEs) */
>> - nes_write32(nesdev->regs+NES_WQE_ALLOC, 0x05800000 | nesdev->cqp.qp_id);
>> + nes_write32_relaxed(nesdev->regs+NES_WQE_ALLOC,
>> + 0x05800000 | nesdev->cqp.qp_id);
>
> barrier() is not strong enough to order writel, so this doesn't seem
> right?
>
> It is probably noteven strong enough for what this driver thinks it is
> doing.. This driver is essentially dead and broken, probably just
> don't change it.
Just for the sake of other changes in netdev directory and my education...
barrier() on ARM is a wmb(). It should be a compiler barrier on intel.
You are saying barrier() should have been a wmb(), right?
I have gone through similar exercise on netdev directory and changed
barrier()
writel()
to
barrier()
writel_relaxed()
Do you see any problem with this?
If the goal is to make memory changes observable to the hardware, it should
have been, right not barrier()?
wmb()
writel_relaxed()
>
> Jason
>
--
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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