linux-kernel - Re: [PATCH 4/5] mtd: spi-nor: Add driver for Adaptrum Anarion QSPI controller

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Date:   Mon, 31 Jul 2017 15:20:23 -0700
From:   Alexandru Gagniuc <alex.g@...ptrum.com>
To:     Marek Vasut <marek.vasut@...il.com>,
        linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Richard Weinberger <richard@....at>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 4/5] mtd: spi-nor: Add driver for Adaptrum Anarion QSPI
 controller

On 07/31/2017 02:33 PM, Marek Vasut wrote:
> On 07/31/2017 07:17 PM, Alexandru Gagniuc wrote:

Hi Marek,

Thank you again for your feedback. I've applied a majority of your 
suggestions, and I am very happy with the result. I should have v2 
posted within a day or so.

[snip]
>>>> +/*
>>>> + * This mask does not match reality. Get over it:
>>>
>>> What is this about ?
>>
>> Each stage of the QSPI chain has two registers. The second register has
>> a bitfield which takes in the length of the stage. For example, for
>> DATA2, we can set the length up to 0x4000, but for ADDR2, we can only
>> set a max of 4 bytes. I wrote this comment as a reminder to myself to be
>> careful about using this mask. I'll rephrase the comment for [v2]
>
> Please do.
>
Staged for [PATCH v2]

>>>> + * DATA2:    0x3fff
>>>> + * CMD2:    0x0003
>>>> + * ADDR2:    0x0007
>>>> + * PERF2:    0x0000
>>>> + * HI_Z:    0x003f
>>>> + * BCNT:    0x0007
>>>> + */
>>>> +#define CHAIN_LEN(x)        ((x - 1) & ASPI_DATA_LEN_MASK)
>>>> +
>>>> +struct anarion_qspi {
>>>> +    struct        spi_nor nor;
>>>> +    struct        device *dev;
>>>> +    uintptr_t    regbase;
>>>
>>> Should be void __iomem * I guess ?
>>
>> I chose uintptr_t as opposed to void *, because arithmetic on void * is
>> not valid in C. What is the right answer hen, without risking undefined
>> behavior?
>
> What sort of arithmetic ? It's perfectly valid in general ...

ISO/IEC 9899:201x, Section 6.5.6, constraint(2) is not met when the one 
of the operands to addition is a void pointer.
Section 6.2.5 (19) defines void to be an incomplete type.

[snip]

>>> Is this stuff below something like ioread32_rep() ?
>>>
>>>> +    aspi_write_reg(aspi, ASPI_REG_BYTE_COUNT, sizeof(uint32_t));
>>>> +    while (len >= 4) {
>>>> +        data = aspi_read_reg(aspi, ASPI_REG_DATA1);
>>>> +        memcpy(buf, &data, sizeof(data));
>>>> +        buf += 4;
>>>> +        len -= 4;
>>>> +    }
>>
>> That is very similar to ioread32_rep, yes. I kept this as for the
>> reasons outlined above, but changing this to _rep() seems innocent enough.
>
> What reason ?

Being able to share the code between the different codebases where it is 
used.

Alex