linux-kernel - Re: [PATCH 2/2 v2] sata highbank: add bit-banged SGPIO driver support

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Date:	Tue, 4 Jun 2013 13:32:51 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Mark Langsdorf <mark.langsdorf@...xeda.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>
Subject: Re: [PATCH 2/2 v2] sata highbank: add bit-banged SGPIO driver support

Hello, Mark.

On Tue, Jun 04, 2013 at 10:09:41AM -0500, Mark Langsdorf wrote:
> > And tell ahci core sizeof(ecx_host_priv) some way, but really, just
> > having a plain pointer should be enough, I think.
> 
> I think I want to do the opposite. For 90% of the AHCI EM functions,
> I want ecx_host_priv to be an ahci_host_priv so that I can use those
> functions without having to keep a local copy of them.
> 
> Would something like this:
> struct ahci_host_priv {
> 	/* standard AHCI existing stuff */
> 	void *private_data;
> };
> 
> I shied away from that because a private data structure having a private
> data structure doesn't seem right.

Aren't we talking about the same thing?  I'm perfectly fine with
adding a pointer to ahci_host_priv.  Maybe you can name it slightly
differently - say, *impl_data, *platform_data, whatever.

> >> +static ssize_t ecx_transmit_led_message(struct ata_port *ap, u32 state,
> >> +					ssize_t size)
> >> +{
> > ...
> >> +	if (!hpriv->em_msg_type & EM_MSG_TYPE_LED)
> >> +		return size;
> > 
> > Is this really correct?  You first negate and convert it to bool and
> > then bit-wise and it with a mask?  How is supposed to work?
> 
> Am I confused about the order of operations? It's meant to be "continue
> if hpriv->em_msg_type doesn't have EM_MSG_TYPE_LED set".

Shouldn't that be

	if (!(hpriv->em_msg_type & EM_MSG_TYPE_LED))

! has higher priority than &.  You're converting em_msg_type to 1 or 0
  and then and'ing EM_MSG_TYPE_LED to it.

> >> -	ahci_save_initial_config(dev, hpriv, 0, 0);
> >> +	ahci_save_initial_config(dev, (struct ahci_host_priv *) hpriv, 0, 0);
> > 
> > Ugh....... how is this supposed to work?  What if ahci_host_priv grows
> > larger than ecx one in the future? :(
> 
> For functions like ahci_save_initial_config, I just want to use the
> already defined ahci_ functions with my extra data along for the ride.
> What's the best way to do that?

Please don't override different types on the same area.  Having the
driver specific data in a separate struct pointed to by ahci_host_priv
should work fine, right?

Thanks.

-- 
tejun
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