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

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Message-ID: <20200528143847.vd7b434xtgiaobv4@mobilestation>
Date:   Thu, 28 May 2020 17:38:47 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Vignesh Raghavendra <vigneshr@...com>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Maxim Kaurkin <Maxim.Kaurkin@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Ramil Zaripov <Ramil.Zaripov@...kalelectronics.ru>,
        Ekaterina Skachko <Ekaterina.Skachko@...kalelectronics.ru>,
        Vadim Vlasov <V.Vlasov@...kalelectronics.ru>,
        Alexey Kolotnikov <Alexey.Kolotnikov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Arnd Bergmann <arnd@...db.de>,
        Lee Jones <lee.jones@...aro.org>, <linux-mips@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mtd@...ts.infradead.org>
Subject: Re: [PATCH RESEND v2] mtd: physmap: Add Baikal-T1 physically mapped
 ROMs support

On Thu, May 28, 2020 at 04:35:41PM +0530, Vignesh Raghavendra wrote:
> 
> 
> 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

Agreed. I'll remove the Baikal-T1 Boot ROM support in the next version.

-Sergey