linux-kernel - Re: [PATCH 1/1] block: IBM RamSan 70/80 driver fixes.

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Date:	Tue, 19 Feb 2013 09:40:51 -0600
From:	"Philip J. Kelleher" <pjk1939@...ux.vnet.ibm.com>
To:	Brian King <brking@...ux.vnet.ibm.com>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org,
	josh.h.morris@...ibm.com
Subject: Re: [PATCH 1/1] block: IBM RamSan 70/80 driver fixes.

On Tue, Feb 19, 2013 at 08:18:51AM -0600, Brian King wrote:
> On 02/18/2013 02:00 PM, Philip J. Kelleher wrote:
> > diff -uprN -X linux-block-vanilla/Documentation/dontdiff linux-block-vanilla/drivers/block/rsxx/config.c linux-block/drivers/block/rsxx/config.c
> > --- linux-block-vanilla/drivers/block/rsxx/config.c	2013-02-12 11:25:37.756352070 -0600
> > +++ linux-block/drivers/block/rsxx/config.c	2013-02-15 09:01:43.221166194 -0600
> > @@ -31,7 +31,7 @@
> > 
> >  static void initialize_config(void *config)
> >  {
> > -	struct rsxx_card_cfg *cfg = (struct rsxx_card_cfg *) config;
> > +	struct rsxx_card_cfg *cfg = config;
> 
> Why not pass a struct rsxx_card_cfg * here instead of a void*?
> 
> 
> 

Alright, I guess that makes it more readable.

> > @@ -126,7 +126,11 @@ static void creg_issue_cmd(struct rsxx_c
> >  					  cmd->buf, cmd->stream);
> >  	}
> > 
> > -	/* Data copy must complete before initiating the command. */
> > +	/*
> > +	 * Data copy must complete before initiating the command. This is
> > +	 * needed for weakly ordered processors (i.e. PowerPC), so that all
> > +	 * neccessary registers are written before we kick the hardware.
> > +	 */
> >  	wmb();
> 
> When you say data copy are you referring to the writes to the host DMA
> buffer that occurred previously? If so, the iowrite / writel macros
> already ensure this, as they have a sync instruction built in to them
> to cover this case, so a wmb would be redundant.
> 
> If its to ensure that all the iowrite's make it to the device as one
> transaction and don't get interleaved with some other iowrite's, as
> long as you have a spinlock protecting these writes, the PowerPC
> spin_unlock will guarantee an mmiowb, so this shouldn't be an issue
> either.
> 
> 

Alright, I'll look into it. Again, I just needed to make sure that the
proper register were written before I kick off the HW.

> > diff -uprN -X linux-block-vanilla/Documentation/dontdiff linux-block-vanilla/drivers/block/rsxx/rsxx.h linux-block/drivers/block/rsxx/rsxx.h
> > --- linux-block-vanilla/drivers/block/rsxx/rsxx.h	2013-02-12 11:25:37.780170779 -0600
> > +++ linux-block/drivers/block/rsxx/rsxx.h	2013-02-18 08:54:59.692973434 -0600
> > @@ -35,6 +35,8 @@ struct rsxx_reg_access {
> >  	__u32 data[8];
> >  };
> > 
> > +#define RSXX_MAX_REG_CNT	(8 * (sizeof(__u32)))
> 
> Is this 8 related to the 8 in the array above? If so, why not have a literal
> to define the 8 and use it in both places to make this clear?
> 

Alright.

> -Brian
> 
> -- 
> Brian King
> Power Linux I/O
> IBM Linux Technology Center
> 
> 

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