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

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Date:   Mon, 09 Mar 2020 19:31:03 +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 19:14, 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 ;)

>> 
>> > 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.

Btw. do other SoCs perform better with DMA?

-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