linux-kernel - Re: [PATCH v2 3/6] spi: dw: Add Microchip Sparx5 support

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Date:   Mon, 22 Jun 2020 12:46:33 +0200
From:   Lars Povlsen <lars.povlsen@...rochip.com>
To:     Mark Brown <broonie@...nel.org>
CC:     Lars Povlsen <lars.povlsen@...rochip.com>,
        SoC Team <soc@...nel.org>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        <linux-spi@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        "Serge Semin" <fancer.lancer@...il.com>,
        Serge Semin <Sergey.Semin@...kalelectronics.ru>
Subject: Re: [PATCH v2 3/6] spi: dw: Add Microchip Sparx5 support


Mark Brown writes:

On Fri, Jun 19, 2020 at 01:31:18PM +0200, Lars Povlsen wrote:

>> +/*
>> + * The Designware SPI controller (referred to as master in the
>> + * documentation) automatically deasserts chip select when the tx fifo
>> + * is empty. The chip selects then needs to be driven by a CS override
>> + * register. enable is an active low signal.
>> + */
>> +static void dw_spi_sparx5_set_cs(struct spi_device *spi, bool nEnable)
>
>The value that is passed in here is the value that should be driven on
>the output pin, the driver should not be interpreting the value in any
>way here.  Documenting it as nEnable adds a layer of confusion, and it
>may not be an active high signal depending on the system.

Ok, I will make the CS function more like the others.

>
>> +	if (!nEnable) {
>> +		/* Ensure CS toggles, so start off all disabled */
>> +		regmap_write(dwsmscc->syscon, SPARX5_FORCE_VAL, ~0);
>> +		/* CS override drive enable */
>> +		regmap_write(dwsmscc->syscon, SPARX5_FORCE_ENA, 1);
>
>This should just be setting the value to whatever the core asked for it
>to be set to, the driver adding extra toggles is likely to disrupt
>things.

I will have a look at this again. But it was added for a reason. The
issue is that we have two different busses in front of the controller,
so we might need more settle time when switching interface.

Thank you for you comments,

Cheers

-- 
Lars Povlsen,
Microchip