[PATCH] mtd: bcm47xxsflash: support reading flash out of mapping window

[Rafał Miłecki]

On 17 January 2017 at 10:49, Marek Vasut <marek.vasut at gmail.com> wrote:
> On 01/17/2017 07:58 AM, Rafał Miłecki wrote:
>> On 17 January 2017 at 04:18, Marek Vasut <marek.vasut at gmail.com> wrote:
>>> On 01/16/2017 11:09 PM, Rafał Miłecki wrote:
>>>> From: Rafał Miłecki <rafal at milecki.pl>
>>>>
>>>> For reading flash content we use MMIO but it's possible to read only
>>>> first 16 MiB this way. It's simply an arch design/limitation.
>>>> To support flash sizes bigger than 16 MiB implement indirect access
>>>> using ChipCommon registers.
>>>> This has been tested using MX25L25635F.
>>>>
>>>> Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
>>>> ---
>>>>  drivers/mtd/devices/bcm47xxsflash.c | 12 +++++++++++-
>>>>  drivers/mtd/devices/bcm47xxsflash.h |  3 +++
>>>>  2 files changed, 14 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/mtd/devices/bcm47xxsflash.c b/drivers/mtd/devices/bcm47xxsflash.c
>>>> index 4decd8c..5d57119 100644
>>>> --- a/drivers/mtd/devices/bcm47xxsflash.c
>>>> +++ b/drivers/mtd/devices/bcm47xxsflash.c
>>>> @@ -110,7 +110,17 @@ static int bcm47xxsflash_read(struct mtd_info *mtd, loff_t from, size_t len,
>>>>       if ((from + len) > mtd->size)
>>>>               return -EINVAL;
>>>>
>>>> -     memcpy_fromio(buf, b47s->window + from, len);
>>>> +     if (from + len <= BCM47XXSFLASH_WINDOW_SIZE) {
>>>> +             memcpy_fromio(buf, b47s->window + from, len);
>>>> +     } else {
>>>> +             size_t i;
>>>> +
>>>> +             for (i = 0; i < len; i++) {
>>>> +                     b47s->cc_write(b47s, BCMA_CC_FLASHADDR, from++);
>>>> +                     bcm47xxsflash_cmd(b47s, OPCODE_ST_READ4B);
>>>> +                     *(buf++) = b47s->cc_read(b47s, BCMA_CC_FLASHDATA) & 0xff;
>>>
>>> Do you really need to send command on every write into the FLASHADDR
>>> register ? Doesn't this hardware support some sort of seqeuntial reading?
>>
>> Yes, I need to. If there is some other way it's undocumented and not
>> used by Broadcom. As a quick check I tried not writing to FLASHADDR
>> every time, but it didn't work.
>
> Oh well, that's a bit sad. Thanks for checking.
>
>>> Are you sure this has no side-effects when you mix this with reading
>>> from the flash window ?
>>
>> No side effects. I also tried reading whole flash content using this
>> indirect access and it worked as well.
>
> Well, if you read the whole flash, you will trigger the first windowed
> read and then the new code, in sequence. Try doing some read pattern
> where you read from the beginning and mix it with reads from the end.
> That will alternate between these two bits of code.

I really can't follow your possible-fail scenario. With my patch first
16 MiB are read using windowed access, another 16 MiB using indirect
access. I scanned whole flash this way, it worked. I got a working
system. It just works...