Re: [PATCH RESEND v2] mtd: physmap: Add Baikal-T1 physically mapped ROMs support

From: Vignesh Raghavendra
Date: Thu May 28 2020 - 07:06:13 EST

On 28/05/20 4:12 pm, Serge Semin wrote:
>>> +
>>> +static map_word __xipram bt1_rom_dummy_read(struct map_info *map,
>>> + unsigned long ofs)
>>> +{
>>> + map_word ret;
>>> +
>>> + ret.x[0] = 0xFF;
>>> +
>>> + return ret;
>>> +}
>> Why define dummy_io for "baikal,bt1-boot-rom"? I don't see any use of
>> adding a driver that always reads 0xFFs
> This is supposed to be temporary solution for the baikal,bt1-boot-rom ROM.
> The Boot ROM mirror might reflect either an embedded firmware or the SPI flash
> directly mapped into the memory. In former case there is no problem, we can
> freely read from the Boot ROM region. But in the later case the mirrored region
> (memory mapped SPI flash) is not always accessible. If normal Boot SPI
> controller is enabled, then the SPI flash mapping isn't accessible (any attempt
> will cause a bus-error). In order to fix this we'd need a mutual exclusive lock,
> which would disable the SPI controller while the mirrored memory mapped SPI flash
> region needs to be accessed. Such mechanism isn't currently implemented, but it
> will in be in the framework of my patch created for the SPI subsystem.
> My idea was to just provide a dummy callback for now and replace it with normal
> IO-methods with mutual exclusive lock-unlocks when the corresponding SPI driver
> is accepted.

Yes I understand, but I don't see any advantage for end user by
providing dummy calls... So please don't add the callbacks until they
implement proper functionality