linux-kernel - Re: [PATCH v2] drivers/soc/litex: remove 8-bit subregister option

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Date:   Fri, 11 Jun 2021 04:45:48 +0900
From:   Stafford Horne <shorne@...il.com>
To:     "Gabriel L. Somlo" <gsomlo@...il.com>
Cc:     Joel Stanley <joel@....id.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Karol Gugala <kgugala@...micro.com>,
        Mateusz Holenko <mholenko@...micro.com>,
        pczarnecki@...ernships.antmicro.com,
        David Gow <davidgow@...gle.com>,
        Florent Kermarrec <florent@...oy-digital.fr>
Subject: Re: [PATCH v2] drivers/soc/litex: remove 8-bit subregister option

On Wed, May 26, 2021 at 11:17:36PM -0400, Gabriel L. Somlo wrote:
> On Thu, May 27, 2021 at 02:12:40AM +0000, Joel Stanley wrote:
> > On Wed, 26 May 2021 at 10:55, Gabriel Somlo <gsomlo@...il.com> wrote:
> > >
> > > Since upstream LiteX recommends that Linux support be limited to
> > > designs configured with 32-bit CSR subregisters (see commit a2b71fde
> > > in upstream LiteX, https://github.com/enjoy-digital/litex), remove
> > > the option to select 8-bit subregisters, significantly reducing the
> > > complexity of LiteX CSR (MMIO register) accessor methods.
> > >
> > > NOTE: for details on the underlying mechanics of LiteX CSR registers,
> > > see https://github.com/enjoy-digital/litex/wiki/CSR-Bus or the original
> > > LiteX accessors (litex/soc/software/include/hw/common.h in the upstream
> > > repository).
> > >
> > > Signed-off-by: Gabriel Somlo <gsomlo@...il.com>
> > 
> > I like how this simplifies things.
> > 
> > Reviewed-by: Joel Stanley <joel@....id.au>
> 
> Thanks!
>  
> > With this change, is there any need to keep the litex acessors around?
> > 
> > There's the 64 bit case, but we don't have any 64 bit CSR registers do we?
>  
> Off the top of my head, the LiteSDcard driver uses 64-bit CSR writes:
> https://github.com/litex-hub/linux/blob/litex-rebase/drivers/mmc/host/litex_mmc.c#L403
> and
> https://github.com/litex-hub/linux/blob/litex-rebase/drivers/mmc/host/litex_mmc.c#L421
> 
> These are both DMA base-address registers that support rv64*.
> 

I have pushed version to to for-next which should show up in linux-next today or
next week.

-Stafford