linux-kernel - Re: [RFC PATCH] spi: Take the SPI IO-mutex in the spi

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Date:   Fri, 20 Nov 2020 20:26:21 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Ramil Zaripov <Ramil.Zaripov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] spi: Take the SPI IO-mutex in the spi_setup() method

On Fri, Nov 20, 2020 at 05:17:48PM +0000, Mark Brown wrote:
> On Tue, Nov 17, 2020 at 12:45:17PM +0300, Serge Semin wrote:
> 
> > Of course I could have provided a fix affecting the DW APB SSI driver
> > only, for instance, by creating a mutual exclusive access to the set_cs
> > callback and setting/clearing only the bit responsible for the
> > corresponding chip-select. But after a short research I've discovered that
> 

> I think the driver needs a fix anyway for the case where there's a mix
> of devices with standard and inverted chip selects, it assumes they all
> have the same polarity AFAICT.

No. The polarity inversion isn't supported by the DW APB SSI
controller. Native chip-select is always active-low, while a
corresponding peripheral is activated by setting a bit in the SER
register (Slave Enable Register). So as long as the dw_spi_set_cs()
callback isn't called while there is a SPI-message execution going on
it shall be save do preserve the current version of the method.

-Sergey