linux-kernel - Re: [PATCH v3 50/77] ncr5380: Change instance->host

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Date:	Tue, 22 Dec 2015 08:46:41 +0100
From:	Hannes Reinecke <hare@...e.de>
To:	Finn Thain <fthain@...egraphics.com.au>,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	Michael Schmitz <schmitzmic@...il.com>,
	linux-m68k@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH v3 50/77] ncr5380: Change instance->host_lock to
 hostdata->lock

On 12/22/2015 02:18 AM, Finn Thain wrote:
> NCR5380.c presently uses the instance->host_lock spin lock. Convert this
> to a new spin lock that protects the NCR5380_hostdata struct.
>
> atari_NCR5380.c previously used local_irq_save/restore() rather than a
> spin lock. Convert this to hostdata->lock in irq mode. For SMP platforms,
> the interrupt handler now also acquires the spin lock.
>
> This brings all locking in the two core drivers into agreement.
>
> Adding this locking also means that a bunch of volatile qualifiers can be
> removed from the members of the NCR5380_hostdata struct. This is done in
> a subsequent patch.
>
> Proper locking will allow the abort handler to locate a command being
> aborted. This is presently impossible if the abort handler is invoked when
> the command has been moved from a queue to a pointer on the stack. (If
> eh_abort_handler can't determine whether a command has been completed
> or is still being processed then it can't decide whether to return
> success or failure.)
>
> The hostdata spin lock is now held when calling NCR5380_select() and
> NCR5380_information_transfer(). Where possible, the lock is dropped for
> polling and PIO transfers.
>
> Clean up the now-redundant SELECT_ENABLE_REG writes, that used to provide
> limited mutual exclusion between information_transfer() and reselect().
>
> Accessing hostdata->connected without data races means taking the lock;
> cleanup these accesses.
>
> The new spin lock falls away for m68k and other UP builds, so this should
> have little impact there. In the SMP case the new lock should be
> uncontested even when the SCSI bus is contested.
>
> Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
>
Reviewed-by: Hannes Reinecke <hare@...e.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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