linux-kernel - Re: [PATCH 0/6] NXP DSPI bugfixes and support for LS1028A

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Date:   Mon, 09 Mar 2020 19:59:37 +0100
From:   Michael Walle <michael@...le.cc>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, Esben Haabendal <eha@...f.com>,
        angelo@...am.it, andrew.smirnov@...il.com,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Wei Chen <weic@...dia.com>, Mohamed Hosny <mhosny@...dia.com>,
        peng.ma@....com
Subject: Re: [PATCH 0/6] NXP DSPI bugfixes and support for LS1028A

Am 2020-03-09 19:48, schrieb Vladimir Oltean:
> On Mon, 9 Mar 2020 at 20:31, Michael Walle <michael@...le.cc> wrote:
>> 
>> Am 2020-03-09 19:14, schrieb Vladimir Oltean:
>> > On Mon, 9 Mar 2020 at 20:03, Michael Walle <michael@...le.cc> wrote:
>> >> Am 2020-03-09 15:56, schrieb Vladimir Oltean:
>> >> > From: Vladimir Oltean <vladimir.oltean@....com>
>> >> >
>> >> > This series addresses a few issues that were missed during the previous
>> >> > series "[PATCH 00/12] TCFQ to XSPI migration for NXP DSPI driver", on
>> >> > SoCs other than LS1021A and LS1043A. DMA mode has been completely
>> >> > broken
>> >> > by that series, and XSPI mode never worked on little-endian
>> >> > controllers.
>> >> >
>> >> > Then it introduces support for the LS1028A chip, whose compatible has
>> >> > recently been documented here:
>> >> >
>> >> > https://lore.kernel.org/linux-devicetree/20200218171418.18297-1-michael@walle.cc/
>> >>
>> >> If it is not compatible with the LS1021A the second compatible string
>> >> should be removed. Depending on the other remark about the endianess,
>> >> it might still be compatible, though.
>> >>
>> >
>> > Please feel free to remove it. I wasn't actually planning to add it in
>> > the first place, but now it that it's there it doesn't really bother
>> > anybody either.
>> 
>> But it won't work if the endianess depends on the compatible string ;)
>> 
> 
> True.

So another reason to not have the endianess (read the CMD/TX register 
offset)
depends on the compatible string. Because then it should work also with 
the
ls1021a version, correct?

-michael


> 
>> >>
>> >> > The device tree for the LS1028A SoC is extended with DMA channels
>> >> > definition, such that even though the default operating mode is XSPI,
>> >> > one can simply change DSPI_XSPI_MODE to DSPI_DMA_MODE in the
>> >> > devtype_data structure of the driver and use that instead.
>> >>
>> >> wouldn't it make more sense, to use DMA is the dma node is present
>> >> in the device tree? otherwise use XSPI mode? I don't think it is
>> >> really handy to change the mode inside the driver.
>> >>
>> >
>> > Let's keep it simple. The driver should configure the hardware in the
>> > most efficient and least buggy mode available. Right now that is XSPI.
>> > The hardware description (aka the device tree) is a separate topic. If
>> > there ever arises any situation where there are corner cases with XSPI
>> > mode, it's good to have a fallback in the form of DMA mode, and not
>> > have to worry about yet another problem (which is that there are 2
>> > sets of device tree blobs in deployment).
>> 
>> Point taken. But this is not how other drivers behave, which uses the
>> DMA if its given in the device node.
>> 
> 
> Also true.
> 
>> Btw. do other SoCs perform better with DMA?
>> 
> 
> Not that I know of.
> My general rule of thumb for this controller is: if it supports XSPI
> then use that, otherwise use DMA. Luckily there is just one controller
> that supports none of those, and that would be Coldfire, which uses
> the braindead EOQ mode. I don't have the hardware to do testing on
> that, but in principle if I did, I would have converted that as well
> to the more functional but less efficient TCFQ mode (now removed).
> 
>> -michael
>> 
>> > TL;DR: These DMA channels don't really bother anybody but you never
>> > know when they might come in handy.
>> >
>> >> -michael
>> >>
>> >> >
>> >> > For testing, benchmarking and debugging, the mikroBUS connector on the
>> >> > LS1028A-RDB is made available via spidev.
>> >> >
>> >> > Vladimir Oltean (6):
>> >> >   spi: spi-fsl-dspi: Don't access reserved fields in SPI_MCR
>> >> >   spi: spi-fsl-dspi: Fix little endian access to PUSHR CMD and TXDATA
>> >> >   spi: spi-fsl-dspi: Fix oper_word_size of zero for DMA mode
>> >> >   spi: spi-fsl-dspi: Add support for LS1028A
>> >> >   arm64: dts: ls1028a: Specify the DMA channels for the DSPI
>> >> > controllers
>> >> >   arm64: dts: ls1028a-rdb: Add a spidev node for the mikroBUS
>> >> >
>> >> >  .../boot/dts/freescale/fsl-ls1028a-rdb.dts    | 14 +++++
>> >> >  .../arm64/boot/dts/freescale/fsl-ls1028a.dtsi |  6 +++
>> >> >  drivers/spi/spi-fsl-dspi.c                    | 54 +++++++++++++++----
>> >> >  3 files changed, 64 insertions(+), 10 deletions(-)
>> >
>> > Thanks,
>> > -Vladimir
> 
> -Vladimir