linux-kernel - Re: [PATCH] libahci: fix turning on LEDs in ahci_start

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Message-ID: <20131014132049.GB4722@htj.dyndns.org>
Date:	Mon, 14 Oct 2013 09:20:49 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Lukasz Dorau <lukasz.dorau@...el.com>
Cc:	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libahci: fix turning on LEDs in ahci_start_port()

On Mon, Oct 14, 2013 at 02:58:19PM +0200, Lukasz Dorau wrote:
> If EM Transmit bit is busy during init ata_msleep() is called.
> It is wrong - msleep() should be used instead of ata_msleep(),
> because if EM Transmit bit is busy for one port, it will be busy
> for all other ports too, so using ata_msleep() causes wasting
> tries for another ports.
> 
> The most common scenario looks like that now
> (six ports try to transmit a LED meaasege):
> - port #0 tries for the 1st time and succeeds
> - ports #1-5 try for the 1st time and sleeps
> - port #1 tries for the 2nd time and succeeds
> - ports #2-5 try for the 2nd time and sleeps
> - port #2 tries for the 3rd time and succeeds
> - ports #3-5 try for the 3rd time and sleeps
> - port #3 tries for the 4th time and succeeds
> - ports #4-5 try for the 4th time and sleeps
> - port #4 tries for the 5th time and succeeds
> - port #5 tries for the 5th time and sleeps
> At this moment port #5 wasted all its five tries and failed to initialize.
> Because there are only 5 (EM_MAX_RETRY) tries available usually only five ports
> succeed to initialize. The sixth port and next ones usually will fail.
> 
> If msleep() is used instead of ata_msleep() the first port succeeds to initialize
> in the first try and next ones usually succeed to initialize in the second try.

Ah, interesting.

> Signed-off-by: Lukasz Dorau <lukasz.dorau@...el.com>
> ---
>  drivers/ata/libahci.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
> index acfd0f7..cf38692 100644
> --- a/drivers/ata/libahci.c
> +++ b/drivers/ata/libahci.c
> @@ -779,7 +779,7 @@ static void ahci_start_port(struct ata_port *ap)
>  							       emp->led_state,
>  							       4);
>  				if (rc == -EBUSY)
> -					ata_msleep(ap, 1);
> +					msleep(1);

This is so unobvious.  Can you please add a comment explaining what's
going on?

Thanks.

-- 
tejun
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