linux-kernel - Re: [PATCH 2/2] nvmem: iomap: new driver exposing NVMEM accessible using I/O mapping

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Date:   Fri, 5 Mar 2021 10:33:35 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Rafał Miłecki <rafal@...ecki.pl>,
        Rafał Miłecki <zajec5@...il.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mips@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivek Unune <npcomplete13@...il.com>,
        bcm-kernel-feedback-list@...adcom.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] nvmem: iomap: new driver exposing NVMEM accessible
 using I/O mapping



On 05/03/2021 10:24, Rafał Miłecki wrote:
>>>
>>> +static int iomap_read(void *context, unsigned int offset, void *val,
>>> +              size_t bytes)
>>> +{
>>> +    struct iomap *priv = context;
>>> +    u8 *src = priv->base + offset;
>>> +    u8 *dst = val;
>>> +    size_t tmp;
>>> +
>>> +    tmp = offset % 4;
>>> +    memcpy_fromio(dst, src, tmp);
>>> +    dst += tmp;
>>> +    src += tmp;
>>> +    bytes -= tmp;
>>> +
>>> +    tmp = rounddown(bytes, 4);
>>> +    __ioread32_copy(dst, src, tmp / 4);
>>> +    dst += tmp;
>>> +    src += tmp;
>>> +    bytes -= tmp;
>>> +
>>> +    memcpy_fromio(dst, src, bytes);
>>> +
>>
>>
>> You could just do this!
>>
>>      while (bytes--)
>>          *val++ = readb(priv->base + offset + i++);
> 
> Do you mean that as replacement for "memcpy_fromio" or the whole
> function code?

Yes please!

> The reason for using __ioread32_copy() was to improve reading
> performance (using aligned 32 bit access where possible). I'm not sure
> if that really matters?

Just simple while loop is much readable than the previous code TBH!

> 

> P.S.
> Please don't yell at me in every sentence :( Makes me a bit sad :(
Sorry!! I did not mean anything as such! :-)

--srini