linux-kernel - Re: [PATCH] ahci: enable GHC.AE bit before set GHC.HR

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Date:	Fri, 21 Sep 2007 12:27:36 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Peer Chen <peerchen@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	jeff <jeff@...zik.org>, akpm <akpm@...ux-foundation.org>,
	linux-ide <linux-ide@...r.kernel.org>
Subject: Re: [PATCH] ahci: enable GHC.AE bit before set GHC.HR

On Fri, 21 Sep 2007 12:31:20 +0200
Jens Axboe <jens.axboe@...cle.com> wrote:

> On Fri, Sep 21 2007, Peer Chen wrote:
> > According to the description of section 5.2.2.1 and 10.1.2 of AHCI specification rev1_1/rev1_2, GHC.HR shall only be set to ¡®1¡¯
> > by software when GHC.AE is set to ¡®1¡¯.
> > 
> > Signed-off-by: Peer Chen <peerchen@...il.com>
> > ---
> > --- linux-2.6.23-rc7/drivers/ata/ahci.c.orig	2007-09-20 11:01:55.000000000 -0400
> > +++ linux-2.6.23-rc7/drivers/ata/ahci.c	2007-09-20 11:07:31.000000000 -0400
> > @@ -834,6 +834,10 @@ static int ahci_reset_controller(struct 
> >  	void __iomem *mmio = host->iomap[AHCI_PCI_BAR];
> >  	u32 tmp;
> >  
> > +        /* turn on AHCI mode before controller reset*/
> > +        writel(HOST_AHCI_EN, mmio + HOST_CTL);
> > +        (void) readl(mmio + HOST_CTL);  /* flush */
> > +
> >  	/* global controller reset */
> >  	tmp = readl(mmio + HOST_CTL);
> >  	if ((tmp & HOST_RESET) == 0) {
> 
> I appreciate the readl() flushes, but in this particular case we end up
> reading the exact offset again below.

The code above is wrong btw - it is an iomap so both the new and existing
code should be using ioread* not readl

Alan
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