Re: [PATCH v6 10/10] drivers/char: use smp barriers in xhci driver

[Jan Beulich]

On 02.09.2022 15:17, Marek Marczykowski-Górecki wrote:
> All (interesting) data is in plain WB cached memory, and the few BAR
> register that are configured have a UC mapping, which orders properly
> WRT other writes on x86.
> 
> Suggested-by: Andrew Cooper 
> Signed-off-by: Marek Marczykowski-Górecki 

As said in reply to Andrew's comment: What about non-x86? Drivers like
this one, even if presently depending on X86 in Kconfig, shouldn't be
making assumptions like this. Such is imo only appropriate when a
driver conceivably would only ever be useful on x86.

Jan

[PATCH v6 10/10] drivers/char: use smp barriers in xhci driver

[Marek Marczykowski-Górecki]

All (interesting) data is in plain WB cached memory, and the few BAR
register that are configured have a UC mapping, which orders properly
WRT other writes on x86.

Suggested-by: Andrew Cooper 
Signed-off-by: Marek Marczykowski-Górecki 
---
New in v6
---
 xen/drivers/char/xhci-dbc.c | 20 ++--
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/xen/drivers/char/xhci-dbc.c b/xen/drivers/char/xhci-dbc.c
index 829f1d1d910f..03df4d82a623 100644
--- a/xen/drivers/char/xhci-dbc.c
+++ b/xen/drivers/char/xhci-dbc.c
@@ -666,7 +666,7 @@ static void dbc_pop_events(struct dbc *dbc)
 
 BUILD_BUG_ON((1 << XHCI_TRB_SHIFT) != sizeof(struct xhci_trb));
 
-rmb();
+smp_rmb();
 
 while ( xhci_trb_cyc(event) == er->cyc )
 {
@@ -710,7 +710,7 @@ static void dbc_pop_events(struct dbc *dbc)
 }
 
 erdp = er->dma + (er->deq << XHCI_TRB_SHIFT);
-wmb();
+smp_wmb();
 writeq(erdp, >erdp);
 }
 
@@ -847,9 +847,9 @@ static void dbc_enable_dbc(struct dbc *dbc)
 {
 struct dbc_reg *reg = dbc->dbc_reg;
 
-wmb();
+smp_wmb();
 writel(readl(>ctrl) | (1U << DBC_CTRL_DCE), >ctrl);
-wmb();
+smp_wmb();
 
 while ( (readl(>ctrl) & (1U << DBC_CTRL_DCE)) == 0 )
 cpu_relax();
@@ -858,9 +858,9 @@ static void dbc_enable_dbc(struct dbc *dbc)
 if ( !dbc->open )
 dbc_reset_debug_port(dbc);
 
-wmb();
+smp_wmb();
 writel(readl(>portsc) | (1U << DBC_PSC_PED), >portsc);
-wmb();
+smp_wmb();
 
 while ( (readl(>ctrl) & (1U << DBC_CTRL_DCR)) == 0 )
 cpu_relax();
@@ -871,7 +871,7 @@ static void dbc_disable_dbc(struct dbc *dbc)
 struct dbc_reg *reg = dbc->dbc_reg;
 
 writel(readl(>portsc) & ~(1U << DBC_PSC_PED), >portsc);
-wmb();
+smp_wmb();
 writel(readl(>ctrl) & ~(1U << DBC_CTRL_DCE), >ctrl);
 
 while ( readl(>ctrl) & (1U << DBC_CTRL_DCE) )
@@ -1032,7 +1032,7 @@ static bool dbc_ensure_running(struct dbc *dbc)
 {
 writel(ctrl | (1U << DBC_CTRL_DRC), >ctrl);
 writel(readl(>portsc) | (1U << DBC_PSC_PED), >portsc);
-wmb();
+smp_wmb();
 dbc_ring_doorbell(dbc, dbc->dbc_iring.db);
 dbc_ring_doorbell(dbc, dbc->dbc_oring.db);
 }
@@ -1074,7 +1074,7 @@ static void dbc_flush(struct dbc *dbc, struct 
xhci_trb_ring *trb,
 }
 }
 
-wmb();
+smp_wmb();
 dbc_ring_doorbell(dbc, trb->db);
 }
 
@@ -1101,7 +1101,7 @@ static void dbc_enqueue_in(struct dbc *dbc, struct 
xhci_trb_ring *trb,
 dbc_push_trb(dbc, trb, wrk->dma + wrk->enq,
  dbc_work_ring_space_to_end(wrk));
 
-wmb();
+smp_wmb();
 writel(db, >db);
 }
 
-- 
git-series 0.9.1