Re: [PATCH v4 17/19] mtd: rawnand: Introduce nand_choose_best_vendor_sdr_iface()

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Rickard,

Rickard X Andersson <Rickard.Andersson@axis.com> wrote on Tue, 26 May
2020 09:35:38 +0000:

> On Mon, May 25, 2020 at 7:47 PM Miquel Raynal <miquel.raynal@bootlin.com> wrote:
> 
> > +/**
> > + * nand_choose_best_sdr_iface - given a data interface, find the closest
> > + *                              mode/timings set for this interface supported
> > + *                              by both the NAND controller and the NAND chip
> > + * @chip: the NAND chip
> > + * @best_iface: the best data interface (can eventually be updated)
> > + */
> > +static int nand_choose_best_sdr_iface(struct nand_chip *chip,
> > +                                     struct nand_data_interface *best_iface)
> > +{
> > +       const struct nand_controller_ops *ops = chip->controller->ops;
> > +       int mode, ret;
> > +
> > +       /* Verify the controller supports the requested interface */
> > +       ret = ops->setup_data_interface(chip, NAND_DATA_IFACE_CHECK_ONLY,
> > +                                       best_iface);
> > +       if (!ret)
> > +               return ret;
> > +
> > +       /* Fallback to slower modes */
> > +       for (mode = best_iface->timings.mode - 1; mode >= 0; mode--) {
> > +               ret = onfi_fill_data_interface(chip, best_iface,
> > +                                              NAND_SDR_IFACE, mode);
> > +               if (ret)
> > +                       continue;
> > +
> > +               ret = ops->setup_data_interface(chip,
> > +                                               NAND_DATA_IFACE_CHECK_ONLY,
> > +                                               best_iface);
> > +               if (!ret)
> > +                       break;
> > +       }
> > +
> > +       return 0;
> > +}
> > +  
> 
> Should we not start looping from "mode = best_iface->timings.mode" ? The first setup_data_interface call in the above function tests the specific timings or am I missing something?

Indeed, we assume that the controller driver will not support the
"official" ONFI timings mode X if it did not support the specific
timings close to mode X.

This is an assumption, but I don't think we are far from the reality
here.

Miquèl

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