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

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Message-ID: <0e7da44f-c41b-de15-62c3-7509e556f623@gmail.com>
Date:   Wed, 29 Mar 2017 15:57:38 +0200
From:   Marek Vasut <marek.vasut@...il.com>
To:     Ludovic BARRE <ludovic.barre@...com>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Richard Weinberger <richard@....at>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 2/2] mtd: spi-nor: add driver for STM32 quad spi flash
 controller

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 ?

> 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;
>>>>> +}
>>>> [...]
>>>>
>>
> 


-- 
Best regards,
Marek Vasut