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

From: Ben Dooks <ben.dooks@codethink.co.uk>
To: Atish Patra <atishp@atishpatra.org>
Cc: Cyril.Jean@microchip.com, devicetree@vger.kernel.org,
	Albert Ou <aou@eecs.berkeley.edu>,
	Daire McNamara <Daire.McNamara@microchip.com>,
	Anup Patel <anup.patel@wdc.com>,
	"linux-kernel@vger.kernel.org List"
	<linux-kernel@vger.kernel.org>, Atish Patra <atish.patra@wdc.com>,
	Rob Herring <robh+dt@kernel.org>,
	Alistair Francis <alistair.francis@wdc.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	Padmarao Begari <Padmarao.Begari@microchip.com>
Subject: Re: [RFC PATCH 2/3] RISC-V: Initial DTS for Microchip ICICLE board
Date: Tue, 3 Nov 2020 18:39:09 +0000	[thread overview]
Message-ID: <22800ecc-a91b-ee3c-4717-4ee8802f31a2@codethink.co.uk> (raw)
In-Reply-To: <CAOnJCUKH77XDymG+jAUYHP+5TC2aabTR4f8jF6s6FqqQNR=_CQ@mail.gmail.com>

On 03/11/2020 18:36, Atish Patra wrote:
> On Tue, Nov 3, 2020 at 10:28 AM Ben Dooks <ben.dooks@codethink.co.uk> wrote:
>>
>> On 03/11/2020 18:10, Cyril.Jean@microchip.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@codethink.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.

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

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