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SubjectRe: [PATCH v3 18/18] infiniband: cxgb4: Eliminate duplicate barriers on weakly-ordered archs
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On 3/17/2018 12:03 AM, Sinan Kaya wrote:
> On 3/16/2018 11:40 PM, Sinan Kaya wrote:
>> I'll change writel_relaxed() with __raw_writel() in the series like you suggested
>> and also look at your other comments.
>
> I spoke too soon.
>
> Now that I realized, code needs to follow one of the following patterns for correctness
>
> 1)
> wmb()
> writel()/writel_relaxed()
>
> or
>
> 2)
> wmb()
> __raw_wrltel()
> mmiowb()
>
> but definitely not
>
> wmb()
> __raw_wrltel()
>
> Since #1 == #2, I'll stick to my current implementation of writel_relaxed()
>
> Changing writel() to writel_relaxed() or __raw_writel() isn't enough. PowerPC needs mmiowb()
> for correctness. ARM's mmiowb() implementation is empty.
>
> So, there is no one size fits all solution with the current state of affairs.
>
>

I think I finally got what you mean.

Code seems to have

wmb()
writel()/writeq()
wmb()

this can be safely replaced with

wmb()
__raw_writel()/__raw_writeq()
wmb()

This will work on all arches. Below is the new version. Let me know if this is OK.

+++ b/drivers/infiniband/hw/cxgb4/t4.h
@@ -457,7 +457,7 @@ static inline void pio_copy(u64 __iomem *dst, u64 *src)
int count = 8;

while (count) {
- writeq(*src, dst);
+ __raw_writeq(*src, dst);
src++;
dst++;
count--;
@@ -477,15 +477,16 @@ static inline void t4_ring_sq_db(struct t4_wq *wq, u16 inc, union t4_wr *wqe)
(u64 *)wqe);
} else {
pr_debug("DB wq->sq.pidx = %d\n", wq->sq.pidx);
- writel(PIDX_T5_V(inc) | QID_V(wq->sq.bar2_qid),
- wq->sq.bar2_va + SGE_UDB_KDOORBELL);
+ __raw_writel(PIDX_T5_V(inc) | QID_V(wq->sq.bar2_qid),
+ wq->sq.bar2_va + SGE_UDB_KDOORBELL);
}

/* Flush user doorbell area writes. */
wmb();
return;
}
- writel(QID_V(wq->sq.qid) | PIDX_V(inc), wq->db);
+ __raw_writel(QID_V(wq->sq.qid) | PIDX_V(inc), wq->db);
+ mmiowmb()
}

static inline void t4_ring_rq_db(struct t4_wq *wq, u16 inc,
@@ -502,15 +503,16 @@ static inline void t4_ring_rq_db(struct t4_wq *wq, u16 inc,
(void *)wqe);
} else {
pr_debug("DB wq->rq.pidx = %d\n", wq->rq.pidx);
- writel(PIDX_T5_V(inc) | QID_V(wq->rq.bar2_qid),
- wq->rq.bar2_va + SGE_UDB_KDOORBELL);
+ __raw_writel(PIDX_T5_V(inc) | QID_V(wq->rq.bar2_qid),
+ wq->rq.bar2_va + SGE_UDB_KDOORBELL);
}

/* Flush user doorbell area writes. */
wmb();
return;
}
- writel(QID_V(wq->rq.qid) | PIDX_V(inc), wq->db);
+ __raw_writel(QID_V(wq->rq.qid) | PIDX_V(inc), wq->db);
+ mmiowmb();
}


--
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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