linux-kernel - Re: [PATCH v8] mtd: spi-nor: Add support for S3AN spi-nor devices

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Date:   Thu, 1 Dec 2016 19:11:24 +0100
From:   Marek Vasut <marek.vasut@...il.com>
To:     Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
Cc:     Cyrille Pitchen <cyrille.pitchen@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Richard Weinberger <richard@....at>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8] mtd: spi-nor: Add support for S3AN spi-nor devices

On 12/01/2016 06:52 PM, Ricardo Ribalda Delgado wrote:
> Hi Marek

Hi,

> Thanks for your review
> 
> On Thu, Dec 1, 2016 at 5:05 PM, Marek Vasut <marek.vasut@...il.com> wrote:
>>
>> On 11/24/2016 05:56 PM, Ricardo Ribalda Delgado wrote:
> 
>>> +#define      SPI_S3AN                BIT(10) /*
>>> +                                      * Xilinx Spartan 3AN In-System Flash
>>> +                                      * (MFR cannot be used for probing
>>> +                                      * because it has the same value as
>>> +                                      * ATMEL flashes)
>>> +                                      */
>>
>> I have possibly off-topic question. Altera has something very similar --
>> EPCS/EPCQ flash which cannot be detected using standard READID .
>> Would this patch help with supporting those degenerate flashes too?
>>
>>>  };
>>>
> 
> I dont know, but I love the term degenerated flash, please let me use it :)

Hehe. It'd be great to know whether we don't have a possibility for a
generic usecase here. Can you briefly check that ?

>>>       for (i = 0; i < len; ) {
>>>               ssize_t written;
>>> +             loff_t addr = to + i;
>>> +
>>> +             if (hweight32(nor->page_size) == 1) {
>>> +                     page_offset = addr & (nor->page_size - 1);
>>> +             } else {
>>> +                     uint64_t aux = addr;
>>>
>>> -             page_offset = (to + i) & (nor->page_size - 1);
>>> +                     page_offset = do_div(aux, nor->page_size);
>>> +             }
>>
>> Why is this part necessary ?
> 
> If page_size is not a power of 2 (264,528),  the & (size-1) operation
> for getting the offset  does not work, you need to do a real modulus.

Aaah, now it makes sense. Ew, but all right, thanks for clarifying.
This could use a comment, somewhere along these lines.

>>> +
>>> +     /* Flash in Power of 2 mode */
>>> +     if (val & XSR_PAGESIZE) {
>>> +             nor->page_size = (nor->page_size == 264) ? 256 : 512;
>>
>> 264 is due to some ECC ?
> 
> The flash can be in standard mode or in power of two mode. You need to
> check the status register to know if the chip is in one mode or the
> other.
> 
> The flash is in standard mode from factory, you can change the mode to
> power of two, but the data is corrupted and you cannot change  back to
> standard mode.
> 
> I guess they are using some bits reserved to ECC for data and that way
> you can squeeze some bits for user data.

OK, comment could help clarify this, so please add one.

>>> +             nor->mtd.writebufsize = nor->page_size;
>>> +             nor->mtd.size = 8 * nor->page_size * info->n_sectors;
>>> +             nor->mtd.erasesize = 8 * nor->page_size;
>>> +     } else {
>>> +             nor->flags |= SNOR_F_S3AN_ADDR_DEFAULT;
>>> +     }
>>> +
>>> +     return 0;
>>> +}
>>
>> [...]
>>
>> --
>> Best regards,
>> Marek Vasut
> 
> Thanks Again
> 
> 
> 
> 


-- 
Best regards,
Marek Vasut