Re: [PATCH 2/2] mtd: spi-nor: add driver for STM32 quad spi flash controller

[Ludovic BARRE]

On 03/29/2017 03:57 PM, Marek Vasut wrote:
> On 03/29/2017 03:35 PM, Ludovic BARRE wrote:
>
> [...]
>
> > > > > > +    writel_relaxed(CR_PRESC(presc) | CR_FTHRES(3) | CR_TCEN |
> > > > > > CR_SSHIFT
> > > > > > +               | CR_EN, qspi->io_base + QUADSPI_CR);
> > > > > > +
> > > > > > +    /* a minimum fsize must be set to sent the command id */
> > > > > > +    flash->fsize = 25;
> > > > > I don't understand why this is needed and the comment doesn't make
> > > > > sense. Please fix.
> > > > fsize field defines the size of external memory.
> > > What external memory ? Unclear
> > oops, fsize field defined the size of "flash memory" in stm32 qspi
> > controller.
> Errr, now I am totally lost :) Is that some internal SPI NOR ? Shouldn't
> the size be coming from DT or something ?
>
> > Number of bytes in Flash memory = 2 ^[FSIZE+1].
> > To sent a nor cmd this field must be set (hardware issue),
> > but before "spi_nor_scan" the size of flash nor is not know.
> > So I set a temporary value (workaround).
> Is it needed before the scan ?
yes it's needed before scan (fix a "stm32 qspi controller" issue)

sorry, I try to reformulate:

The nor flash (external component like micron n25q128a13
or spansion s25fl512s ...) is connected to stm32 by classic
spi-nor interface cs, clock and 1/2/4 IO lines.

the stm32 microprocessor has a dedicated controller to
manage spi-nor interface, it's stm32 qspi.

In stm32 qspi controller there is a register with fsize field
which define the size of nor flash (n25q128a13 or s25fl512s...).

fsize can't be null, else the stm32 qspi controller doesn't send
spi-nor command. it's "stm32 qspi controller" issue.

Before the "spi_nor_scan" the size of nor flash (n25q128a13
or s25fl512s...) is not know. So we set a temporary value just
to discover the nor flash with "spi_nor_scan". After we can
set the right value (mtd->size) in fsize.
> > After "spi_nor_scan" the fsize is overwritten by the right value
> > flash->fsize = __fls(mtd->size) - 1;
> > > > Normaly, this field is used only for memory map mode,
> > > > but in fact is check in indirect mode.
> > > > So while flash scan "spi_nor_scan":
> > > > -I can't let 0.
> > > > -I not know yet the size of flash.
> > > > So I fix a temporary value
> > > >
> > > > I will update my comment
> > > Please do, also please consider that I'm reading the comment and I
> > > barely have any clue about this hardware , so make sure I can
> > > understand it.
> > >
> > > > > > +    ret = spi_nor_scan(&flash->nor, NULL, flash_read);
> > > > > > +    if (ret) {
> > > > > > +        dev_err(qspi->dev, "device scan failed\n");
> > > > > > +        return ret;
> > > > > > +    }
> > > > > > +
> > > > > > +    flash->fsize = __fls(mtd->size) - 1;
> > > > > > +
> > > > > > +    writel_relaxed(DCR_CSHT(1), qspi->io_base + QUADSPI_DCR);
> > > > > > +
> > > > > > +    ret = mtd_device_register(mtd, NULL, 0);
> > > > > > +    if (ret) {
> > > > > > +        dev_err(qspi->dev, "mtd device parse failed\n");
> > > > > > +        return ret;
> > > > > > +    }
> > > > > > +
> > > > > > +    dev_dbg(qspi->dev, "read mm:%s cs:%d bus:%d\n",
> > > > > > +        qspi->read_mode == CCR_FMODE_MM ? "yes" : "no", cs_num,
> > > > > > width);
> > > > > > +
> > > > > > +    return 0;
> > > > > > +}
> > > > > [...]