linux-kernel - Re: [PATCH v2 00/15] Add support for enhanced SPI for Designware SPI controllers

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Message-ID: <CAHyZL-foBcwQrMy1xAJ7LqnoB8B9DSxwtp6LtvLFBgVwC00avg@mail.gmail.com>
Date:   Thu, 19 Jan 2023 16:26:58 +0000
From:   Sudip Mukherjee <sudip.mukherjee@...ive.com>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Mark Brown <broonie@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        jude.onyenegecha@...ive.com, ben.dooks@...ive.com,
        jeegar.lakhani@...ive.com, linux-spi@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/15] Add support for enhanced SPI for Designware SPI controllers

On Mon, Jan 9, 2023 at 4:25 PM Serge Semin <fancer.lancer@...il.com> wrote:
>
> Hello Sudip
>
> On Thu, Jan 05, 2023 at 01:20:39AM +0300, Serge Semin wrote:
> > Hi Sudip
> >
> > On Sun, Dec 18, 2022 at 08:45:26PM +0300, Serge Semin wrote:
> > > Hi Sudip
> > >
> > > On Mon, Dec 12, 2022 at 06:07:17PM +0000, Sudip Mukherjee wrote:
> > > > The is v2 of the patch series adding enhanced SPI support. Some Synopsys SSI
> > > > controllers support enhanced SPI which includes Dual mode, Quad mode and
> > > > Octal mode. DWC_ssi includes clock stretching feature in enhanced SPI modes
> > > > which can be used to prevent FIFO underflow and overflow conditions while
> > > > transmitting or receiving the data respectively.
> > > >
> > > > This is almost a complete rework based on the review from Serge.
> > >
> > > Thank you very much for the series. I'll have a look at it on the next
> > > week.
> >
> > Just so you know. I haven't forgot about the series. There are some
> > problematic parts which I need to give more thinking than I originally
> > expected. I'll submit my comments very soon. Sorry for the delay.
> >
> > Good news is that I've got the HW-manual for the DW SSI v1.01a
> > IP-core. So I'll no longer need to ask of you about that device
> > implementation specifics.
>
> Finally I managed to consolidate my thoughts regarding your patchset.
> Here is the summary. Some specific comments will be sent in-reply to
> the corresponding patches.
>
> First of all there is a crucial difference between eSPI capability
> available on DW APB SSI and DW AHB SSI controllers:
> DW APB SSI 4.x:
> + Tx until FIFO is empty
> + No clock stretching at all

Thanks for your detailed review and all the additional details about
DW APB SSI. I did not have this datasheet to check.
So, that will mean I can remove the APB versiom detection from my next series.
But unfortunately, I don't have access to the hardware currently to
prepare and test the v3 series. It will be delayed a bit and I am
hoping I will be able to work on this by early March.


-- 
Regards
Sudip