linux-kernel - Re: [RFC PATCH 2/3] RISC-V: Initial DTS for Microchip ICICLE board

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Date:   Tue, 3 Nov 2020 10:45:24 -0800
From:   Atish Patra <atishp@...shpatra.org>
To:     Ben Dooks <ben.dooks@...ethink.co.uk>
Cc:     Cyril.Jean@...rochip.com, devicetree@...r.kernel.org,
        Albert Ou <aou@...s.berkeley.edu>,
        Daire McNamara <Daire.McNamara@...rochip.com>,
        Anup Patel <anup.patel@....com>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Atish Patra <atish.patra@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Alistair Francis <alistair.francis@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Padmarao Begari <Padmarao.Begari@...rochip.com>
Subject: Re: [RFC PATCH 2/3] RISC-V: Initial DTS for Microchip ICICLE board

On Tue, Nov 3, 2020 at 10:39 AM Ben Dooks <ben.dooks@...ethink.co.uk> wrote:
>
> On 03/11/2020 18:36, Atish Patra wrote:
> > On Tue, Nov 3, 2020 at 10:28 AM Ben Dooks <ben.dooks@...ethink.co.uk> wrote:
> >>
> >> On 03/11/2020 18:10, Cyril.Jean@...rochip.com wrote:
> >>> On 11/3/20 3:07 PM, Atish Patra wrote:
> >>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >>>>
> >>>> On Fri, Oct 30, 2020 at 2:20 PM Ben Dooks <ben.dooks@...ethink.co.uk> wrote:
> >>
> >> ,snip[
> >>
> >>>>>> @Cyril : Can we enable both eMMC & sdcard at the same time ?
> >>>>> I would put /both/ in but only enable the one in use for the moment.
> >>>>> Our boards are booting of eMMC as supplied, so this isn't going to work
> >>>>> as well. The eMMC is 8bit wide, and thus is only delivering 11MB/sec
> >>>>> instead of 22MB/sec. This performance is still not great, but losing
> >>>>> half the data-rate is just not good.
> >>>>>
> >>>> I am not sure what should be enabled by default. Updating sdcard is much
> >>>> easier than eMMC card and we use that approach.
> >>>>
> >>>> @Cyril: Is there a way that we can enable both ?
> >>>>
> >>> Yes, we can enable both but this requires a modification to the FPGA
> >>> design. One of the guys prototyped this while I was away. We will move
> >>> this along. This will require reprogramming the FPGA with a new design
> >>> and HSS version.
> >>>
> >>> Regards,
> >>>
> >>> Cyril.
> >>
> >> I either missed or couldn't find a way of forcing the boot mode to be
> >> from the SD slot. Have I missed something? At the moment we'd like to
> >> have more storage available as the ~7G free on the eMMC is not enough.
> >>
> >
> > I use tftpboot to load the kernel & DT from the network. SD card is
> > enabled in this DT and Linux
> > kernel uses SD slot instead of eMMC.
> >
> > To summarize, eMMC is used for HSS & U-Boot while SD card is used for
> > Linux which makes
> > more storage available to Linux.
> >
> > IMO, we should enable the sdcard for Linux DT until updated FPGA
> > design & HSS is available.
>
> Interesting as for me the default is for Linux to use the eMMC as
> well. I can't see any way for forcing the selection lines in the
> DT to say eMMC vs SD.
>

because you are probably loading the DT passed by U-boot. I load the DTB
built from the Linux source (the one present in this patch) by
stopping the autoboot in U-Boot.

The DT in U-Boot disables the SD card.


> If there is a way of controlling the selection lines then it might
> be possible to have both cards enabled with a bus selection MUX in
> software.
>
>
> --
> Ben Dooks                               http://www.codethink.co.uk/
> Senior Engineer                         Codethink - Providing Genius
>
> https://www.codethink.co.uk/privacy.html



--
Regards,
Atish