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Date:   Fri, 15 Sep 2023 09:28:20 +0200
From:   =?UTF-8?Q?Rafa=C5=82_Mi=C5=82ecki?= <rafal@milecki.pl>
To:     Scott Branden <scott.branden@broadcom.com>
Cc:     Florian Fainelli <f.fainelli@gmail.com>,
        =?UTF-8?Q?Rafa=C5=82_Mi?= =?UTF-8?Q?=C5=82ecki?= 
        <zajec5@gmail.com>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
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        =?UTF-8?Q?Ar=C4=B1n=C3=A7_=C3=9CNAL?= <arinc.unal@arinc9.com>,
        Florian Fainelli <florian.fainelli@broadcom.com>
Subject: Re: [PATCH] nvmem: brcm_nvram: store a copy of NVRAM content
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On 2023-09-14 23:30, Scott Branden wrote:
> On Thu, Sep 14, 2023 at 2:26 PM Florian Fainelli <f.fainelli@gmail.com> 
> wrote:
>> 
>> On 9/13/23 23:49, Rafał Miłecki wrote:
>> > From: Rafał Miłecki <rafal@milecki.pl>
>> >
>> > This driver uses MMIO access for reading NVRAM from a flash device.
>> > Underneath there is a flash controller that reads data and provides
>> > mapping window.
>> >
>> > Using MMIO interface affects controller configuration and may break real
>> > controller driver. It was reported by multiple users of devices with
>> > NVRAM stored on NAND.
>> >
>> > Modify driver to read & cache all NVRAM content during init and use that
>> > copy to provide NVMEM data when requested.
>> >
>> > Link: https://lore.kernel.org/linux-mtd/CACna6rwf3_9QVjYcM+847biTX=K0EoWXuXcSMkJO1Vy_5vmVqA@mail.gmail.com/
>> > Cc: Arınç ÜNAL <arinc.unal@arinc9.com>
>> > Cc: Florian Fainelli <florian.fainelli@broadcom.com>
>> > Cc: Scott Branden <scott.branden@broadcom.com>
>> > Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
>> > ---
>> [snip]
>> > -     priv->base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
>> > -     if (IS_ERR(priv->base))
>> > -             return PTR_ERR(priv->base);
>> > +     base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
>> > +     if (IS_ERR(base))
>> > +             return PTR_ERR(base);
>> > +
>> > +     priv->size = resource_size(res);
>> > +
>> > +     priv->data = devm_kzalloc(dev, priv->size, GFP_KERNEL);
>> 
>> These can conceivably quite big data structures, how about using 
>> kvmalloc()?
> Why do we even need to expose MMIO interface to NAND though?  Why not
> always go through the controller driver.  I don't see how the MMIO
> access would be used given bad blocks aren't handled?

We need to read NVMRAM *early* for booting purposes. Some vendors store
there information about used firmware in case of having main one and
fallback one. That info is required for partitioning which happens
during mtd initialization before we have NAND driver fully initialized.

-- 
Rafał Miłecki