Subject: Re: [RFC PATCH 20/27] mtd: nand: Let software ECC engines be retrieved from the NAND core

From: Miquel Raynal <[email-masked]>
Date: Mon, 25 Feb 2019 16:49:33 +0100

Hi Boris,

Boris Brezillon <[email-masked]> wrote on Fri, 22 Feb 2019
15:29:57 +0100:

> On Thu, 21 Feb 2019 13:57:59 +0100
> Miquel Raynal <[email-masked]> wrote:
> 
> > Before making use of the ECC engines, we must retrieve them. Add the
> > boilerplate for the ones already available: software engines (Hamming
> > and BCH).
> > 
> > Signed-off-by: Miquel Raynal <[email-masked]>
> > ---
> >  drivers/mtd/nand/ecc/engine.c              | 14 ++++++++++++++
> >  include/linux/mtd/nand-sw-bch-engine.h     |  3 +++
> >  include/linux/mtd/nand-sw-hamming-engine.h |  3 +++
> >  include/linux/mtd/nand.h                   |  3 +++
> >  4 files changed, 23 insertions(+)
> > 
> > diff --git a/drivers/mtd/nand/ecc/engine.c b/drivers/mtd/nand/ecc/engine.c
> > index 7dd3f9772698..318dbb2d56a2 100644
> > --- a/drivers/mtd/nand/ecc/engine.c
> > +++ b/drivers/mtd/nand/ecc/engine.c
> > @@ -286,6 +286,20 @@ bool nand_ecc_correction_is_enough(struct nand_device *nand)
> >  	return corr >= ds_corr && conf->strength >= reqs->strength;
> >  }
> >  
> > +struct nand_ecc_engine *nand_ecc_sw_get_engine(struct nand_device *nand)  
> 
> What if you want to instantiate SW ECC with a custom layout? Can't we
> instead have a function that create a new engine dynamically?
> 
> struct nand_ecc_engine *
> nand_ecc_create_sw_engine(struct nand_device* nand,
> 			  enum nand_ecc_algo algo,
> 			  struct mtd_ooblayout *layout);
> 
> 

Right now, for both sw engines, a default layout is applied if there is
none at engine initialization time.

Also, do we really need a "create" helper? I don't see what's created
there. Maybe you had something else in mind, and the
ecc_sw_xxx_get_engine() approach do not match what you expected, so
please tell me more about your idea, otherwise I don't see what a
nand_ecc_create_sw_engine() would bring.

> 
> > +{
> > +	switch (nand->ecc.user_conf.algo) {  
> 
> Note that the conf is supposed to be passed afterwards, when the ctx is
> created, so you should check nand->ecc.user_conf directly here.

I think this is what I do so I suspect the above sentence is not what
you actually meant?

> 
> > +	case NAND_ECC_HAMMING:
> > +		return ecc_sw_hamming_get_engine();
> > +	case NAND_ECC_BCH:
> > +		return ecc_sw_bch_get_engine();
> > +	default:
> > +		break;
> > +	}
> > +
> > +	return NULL;
> > +}
> > +
> >  MODULE_LICENSE("GPL v2");
> >  MODULE_AUTHOR("Miquel Raynal <[email-masked]>");
> >  MODULE_DESCRIPTION("Generic ECC engine");
> > diff --git a/include/linux/mtd/nand-sw-bch-engine.h b/include/linux/mtd/nand-sw-bch-engine.h
> > index e406aa53ec4e..38cdad117fea 100644
> > --- a/include/linux/mtd/nand-sw-bch-engine.h
> > +++ b/include/linux/mtd/nand-sw-bch-engine.h
> > @@ -11,6 +11,9 @@
> >  #include <linux/mtd/nand.h>
> >  #include <linux/bch.h>
> >  
> > +/* Needed for cross inclusion with nand.h */
> > +struct nand_device;
> > +
> >  /**
> >   * struct ecc_sw_bch_conf - private software BCH ECC engine structure
> >   * @reqooblen: Save the actual user OOB length requested before overwriting it
> > diff --git a/include/linux/mtd/nand-sw-hamming-engine.h b/include/linux/mtd/nand-sw-hamming-engine.h
> > index 8df36d189482..51c5a2acee42 100644
> > --- a/include/linux/mtd/nand-sw-hamming-engine.h
> > +++ b/include/linux/mtd/nand-sw-hamming-engine.h
> > @@ -12,6 +12,9 @@
> >  
> >  #include <linux/mtd/nand.h>
> >  
> > +/* Needed for cross inclusion with nand.h */
> > +struct nand_device;
> > +
> >  /**
> >   * struct ecc_sw_hamming_conf - private software Hamming ECC engine structure
> >   * @reqooblen: Save the actual user OOB length requested before overwriting it
> > diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
> > index 4482eb2bbfd4..3abe113e4f06 100644
> > --- a/include/linux/mtd/nand.h
> > +++ b/include/linux/mtd/nand.h
> > @@ -11,6 +11,8 @@
> >  #define __LINUX_MTD_NAND_H
> >  
> >  #include <linux/mtd/mtd.h>
> > +#include <linux/mtd/nand-sw-hamming-engine.h>
> > +#include <linux/mtd/nand-sw-bch-engine.h>
> >  
> >  struct nand_device;
> >  
> > @@ -253,6 +255,7 @@ struct nand_ecc_engine {
> >  };
> >  
> >  void nand_ecc_read_user_conf(struct nand_device *nand);
> > +struct nand_ecc_engine *nand_ecc_sw_get_engine(struct nand_device *nand);
> >  int nand_ecc_init_ctx(struct nand_device *nand);
> >  void nand_ecc_cleanup_ctx(struct nand_device *nand);
> >  int nand_ecc_prepare_io_req(struct nand_device *nand,  
> 

Thanks,
Miquèl

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