linux-kernel - Re: [PATCH v1] mtd: rawnand: Add Macronix NAND read retry support

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Date:   Tue, 14 May 2019 09:41:00 +0200
From:   Thomas Petazzoni <thomas.petazzoni@...tlin.com>
To:     masonccyang@...c.com.tw
Cc:     bbrezillon@...nel.org, computersforpeace@...il.com,
        dwmw2@...radead.org, juliensu@...c.com.tw,
        linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
        marek.vasut@...il.com, miquel.raynal@...tlin.com, richard@....at
Subject: Re: [PATCH v1] mtd: rawnand: Add Macronix NAND read retry support

Hello,

On Tue, 14 May 2019 09:53:16 +0800
masonccyang@...c.com.tw wrote:

> > > -------------------------------------------------------------------
> > >  static void macronix_nand_onfi_init(struct nand_chip *chip)
> > >  {
> > >           struct nand_parameters *p = &chip->parameters;
> > >           struct nand_onfi_vendor_macronix *mxic = (void 
> > > *)p->onfi->vendor;  
> > 
> > Why cast to void*, instead of casting directly to struct
> > nand_onfi_vendor_macronix * ?  
> 
> Due to got a warning:
> 
>  warning: initialization from incompatible pointer type
>   struct nand_onfi_vendor_macronix *mxic = p->onfi->vendor;

You didn't look at my code, I suggested:

	mxic = (struct nand_onfi_vendor_macronix *) p->info->vendor;

I.e, you indeed still need a cast, because p->info->vendor is a u8[].
But instead of casting to void*, and then implicitly casting to struct
nand_onfi_vendor_macronix *, I suggest to cast directly to struct
nand_onfi_vendor_macronix *.

> > >           if (!p->onfi ||
> > >               ((mxic->reliability_func & MACRONIX_READ_RETRY_BIT) ==   
> 0))
> > >                   return;  
> > 
> > So, the code should be:
> > 
> >    struct nand_onfi_vendor_macronix *mxic;
> > 
> >    if (!p->onfi)
> >       return;
> > 
> >    mxic = (struct nand_onfi_vendor_macronix *) p->info->vendor;
> > 
> >    if ((mxic->reliability_func & MACRONIX_READ_RETRY_BIT) == 0)
> >       return;  
> 
> Also got a warning:
> 
> warning: ISO C90 forbids mixed declarations and code 
> [-Wdeclaration-after-statement]

No, you don't get this warning if you use my code. You get this warning
if you declare and initialized the "mxic" variable at the same location.

>  static void macronix_nand_onfi_init(struct nand_chip *chip)
>  {
>          struct nand_parameters *p = &chip->parameters;
>          struct nand_onfi_vendor_macronix *mxic = (void *)p->onfi->vendor;

You are dereferencing p->info...

> 
>          if (!p->onfi)
>                  return;

... before you check it is NULL. This is wrong.

Please check again the code I sent in my previous e-mail:

    struct nand_onfi_vendor_macronix *mxic;
 
    if (!p->onfi)
       return;
 
    mxic = (struct nand_onfi_vendor_macronix *) p->info->vendor;
 
    if ((mxic->reliability_func & MACRONIX_READ_RETRY_BIT) == 0)
       return;  

Best regards,

Thomas Petazzoni
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com