linux-kernel - Re: [PATCH v4 07/15] mtd: nand: move Samsung specific init/detection logic in nand

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Date:   Sat, 7 Jan 2017 08:49:48 +0100
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Marek Vasut <marek.vasut@...il.com>
Cc:     Richard Weinberger <richard@....at>, linux-mtd@...ts.infradead.org,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>,
        Icenowy Zheng <icenowy@...c.xyz>, Valdis.Kletnieks@...edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 07/15] mtd: nand: move Samsung specific
 init/detection logic in nand_samsung.c

On Sat, 7 Jan 2017 00:53:24 +0100
Marek Vasut <marek.vasut@...il.com> wrote:

> On 01/04/2017 06:08 PM, Boris Brezillon wrote:
> > On Wed, 4 Jan 2017 16:14:07 +0100
> > Marek Vasut <marek.vasut@...il.com> wrote:
> >   
> >> On 01/03/2017 02:01 PM, Boris Brezillon wrote:  
> >>> Move Samsung specific initialization and detection logic into
> >>> nand_samsung.c. This is part of the "separate vendor specific code from
> >>> core" cleanup process.
> >>>
> >>> Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>    
> >>
> >> [...]
> >>  
> >>> diff --git a/drivers/mtd/nand/nand_ids.c b/drivers/mtd/nand/nand_ids.c
> >>> index b3a332f37e14..05e9366696c9 100644
> >>> --- a/drivers/mtd/nand/nand_ids.c
> >>> +++ b/drivers/mtd/nand/nand_ids.c
> >>> @@ -10,7 +10,7 @@
> >>>  #include <linux/mtd/nand.h>
> >>>  #include <linux/sizes.h>
> >>>  
> >>> -#define LP_OPTIONS NAND_SAMSUNG_LP_OPTIONS
> >>> +#define LP_OPTIONS 0
> >>>  #define LP_OPTIONS16 (LP_OPTIONS | NAND_BUSWIDTH_16)
> >>>  
> >>>  #define SP_OPTIONS NAND_NEED_READRDY
> >>> @@ -169,10 +169,12 @@ struct nand_flash_dev nand_flash_ids[] = {
> >>>  };
> >>>  
> >>>  /* Manufacturer IDs */
> >>> +extern const struct nand_manufacturer_ops samsung_nand_manuf_ops;    
> >>
> >> Is the extern needed ?  
> > 
> > Yes, unless you have another solution. If you remove the extern keyword
> > you just redeclare samsung_nand_manuf_ops here, which is not what we
> > want.  
> 
> Maybe some accessor function can help ?
> 

You mean, in nand_ids.c

    const struct nand_manufacturer_ops *get_samsung_nand_mafuf_ops();

    struct nand_manufacturers nand_manuf_ids[] = {
    ...
	{NAND_MFR_SAMSUNG, "Samsung", get_samsung_nand_mafuf_ops},
    ...
    };

and then, in nand_samsung.c

    const struct nand_manufacturer_ops *get_samsung_nand_mafuf_ops()
    {
	return &samsung_nand_mafuf_ops;
    }

What's the point of this extra indirection? I mean, in both cases you
use a symbol that is not part of the same source file, so you'll have
to define this symbol (using a function prototype or an extern object
definition).
Is this all about fixing checkpatch warnings, or do you have a problem
with objects shared between different source files?

Now, I agree that the current approach is not ideal. A real improvement
would be to let the NAND manufacturer drivers (nand_<vendor>.c) register
themselves to the core. Something similar to CLK_OF_DECLARE() or
IRQCHIP_DECLARE() for example. But that means creating a dedicated
section for the nand_manufs_id table, and it's a lot more invasive than
the current approach.