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Re: [PATCH v5 9/9] drivers/char: fix handling cable re-plug in XHCI console driver
- To: Jan Beulich <jbeulich@xxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Fri, 26 Aug 2022 15:44:44 +0000
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- Cc: George Dunlap <George.Dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHYtju+MGvvHxrE+0SJmR6WoIYDR63BSeoAgAAPJAA=
- Thread-topic: [PATCH v5 9/9] drivers/char: fix handling cable re-plug in XHCI console driver
On 26/08/2022 15:50, Jan Beulich wrote:
> On 22.08.2022 17:27, Marek Marczykowski-Górecki wrote:
>> @@ -1023,6 +1032,8 @@ static bool dbc_ensure_running(struct dbc *dbc)
>> writel(ctrl | (1U << DBC_CTRL_DRC), ®->ctrl);
>> writel(readl(®->portsc) | (1U << DBC_PSC_PED), ®->portsc);
>> wmb();
>> + dbc_ring_doorbell(dbc, dbc->dbc_iring.db);
>> + dbc_ring_doorbell(dbc, dbc->dbc_oring.db);
>> }
> You retain the wmb() here, but ...
>
>> @@ -1066,8 +1073,7 @@ static void dbc_flush(struct dbc *dbc, struct
>> xhci_trb_ring *trb,
>> }
>> }
>>
>> - wmb();
>> - writel(db, ®->db);
>> + dbc_ring_doorbell(dbc, trb->db);
>> }
> ... you drop it here. Why the difference?
As a tangent, every single barrier in this file is buggy. Should be
smp_*() variants, not mandatory variants.
All (interesting) data is in plain WB cached memory, and the few BAR
registers which are configured have a UC mapping which orders properly
WRT other writes on x86.
~Andrew
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