linux-kernel - Re: [PATCH V3 2/2] nvmem: add generic driver for devices with MMIO access

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Message-ID: <c4fd4ca4e550bd7de909269e8eedd5f6@milecki.pl>
Date:   Mon, 20 Feb 2023 23:05:01 +0100
From:   Rafał Miłecki <rafal@...ecki.pl>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Rafał Miłecki <zajec5@...il.com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 2/2] nvmem: add generic driver for devices with MMIO
 access

On 2023-02-20 20:55, Randy Dunlap wrote:
> On 2/20/23 09:49, Rafał Miłecki wrote:
>> +static int mmio_nvmem_write(void *context, unsigned int offset, void 
>> *val, size_t bytes)
>> +{
>> +	struct mmio_nvmem *priv = context;
>> +
>> +	switch (priv->io_width) {
>> +	case 1:
>> +	case 2:
>> +	case 4:
>> +		return -EOPNOTSUPP;
> 
> I'm just curious: (since read supports those cases)
> 
> what size writes are typically used here?
> And what value for priv->io_width?

Sorry, I really don't have any statistics on this or any real overview
of hardware that supports MMIO writes. It's probably a minority of
devices that allows it.