linux-kernel - Re: [PATCH] ARM: dts: at91: add serial MFD sub-node for usart

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Message-ID: <20201103085620.GM4488@dell>
Date:   Tue, 3 Nov 2020 08:56:20 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Codrin.Ciubotariu@...rochip.com
Cc:     Nicolas.Ferre@...rochip.com, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        richard.genoud@...il.com, alexandre.belloni@...tlin.com,
        Ludovic.Desroches@...rochip.com
Subject: Re: [PATCH] ARM: dts: at91: add serial MFD sub-node for usart

On Mon, 02 Nov 2020, Codrin.Ciubotariu@...rochip.com wrote:

> On 02.11.2020 14:55, Codrin.Ciubotariu@...rochip.com wrote:
> > On 02.11.2020 14:29, Lee Jones wrote:
> >> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >>
> >> On Mon, 02 Nov 2020, Codrin.Ciubotariu@...rochip.com wrote:
> >>
> >>> On 02.11.2020 11:01, Lee Jones wrote:
> >>>> On Fri, 30 Oct 2020, Nicolas Ferre wrote:
> >>>>
> >>>>> On 30/10/2020 at 12:07, Codrin Ciubotariu wrote:
> >>>>>> The "atmel,at91sam9260-usart" driver is a MFD driver, so it needs sub-nodes
> >>>>>> to match the registered platform device. For this reason, we add a serial
> >>>>>> subnode to all the "atmel,at91sam9260-usart" serial compatible nods. This
> >>>>>> will also remove the boot warning:
> >>>>>> "atmel_usart_serial: Failed to locate of_node [id: -2]"
> >>>>>
> >>>>> I don't remember this warning was raised previously even if the MFD driver
> >>>>> was added a while ago (Sept. 2018).
> >>>>>
> >>>>> I would say it's due to 466a62d7642f ("mfd: core: Make a best effort attempt
> >>>>> to match devices with the correct of_nodes") which was added on mid August
> >>>>> and corrected with 22380b65dc70 ("mfd: mfd-core: Ensure disabled devices are
> >>>>> ignored without error") but maybe not covering our case.
> >>>>>
> >>>>> So, well, I don't know what's the best option to this change. Moreover, I
> >>>>> would say that all other USART related properties go into the child not if
> >>>>> there is a need for one.
> >>>>>
> >>>>> Lee, I suspect that we're not the only ones experiencing this ugly warning
> >>>>> during the boot log: can you point us out how to deal with it for our
> >>>>> existing atmel_serial.c users?
> >>>>
> >>>> You should not be instantiating drivers through Device Tree which are
> >>>> not described there.  If the correct representation of the H/W already
> >>>> exists in Device Tree i.e. no SPI and UART IP really exists, use the
> >>>> MFD core API to register them utilising the platform API instead.
> >>>>
> >>>> This should do it:
> >>>>
> >>>> diff --git a/drivers/mfd/at91-usart.c b/drivers/mfd/at91-usart.c
> >>>> index 6a8351a4588e2..939bd2332a4f6 100644
> >>>> --- a/drivers/mfd/at91-usart.c
> >>>> +++ b/drivers/mfd/at91-usart.c
> >>>> @@ -17,12 +17,10 @@
> >>>>
> >>>>     static const struct mfd_cell at91_usart_spi_subdev = {
> >>>>            .name = "at91_usart_spi",
> >>>> -       .of_compatible = "microchip,at91sam9g45-usart-spi",
> >>>>     };
> >>>>
> >>>>     static const struct mfd_cell at91_usart_serial_subdev = {
> >>>>            .name = "atmel_usart_serial",
> >>>> -       .of_compatible = "atmel,at91rm9200-usart-serial",
> >>>>     };
> >>>>
> >>>>     static int at91_usart_mode_probe(struct platform_device *pdev)
> >>>
> >>> [snip]
> >>>
> >>> Hi Lee, thank you for looking through our usart driver and for sharing
> >>> your thoughts. Removing the usage of compatible string means that for
> >>> similar serial/SPI IPs we would need to create new platform drivers.
> >>
> >> Why would you need to do that?
> > 
> > In the case we will have to support another similar IP, but with a
> > different set of features. Not a new platform driver from scratch, but
> > at least a new struct platform_driver for each variant.
> 
> I guess we could use struct mfd_cell.platform_data to select the 
> features for the serial/SPI. This platform data can be per compatible of 
> our MFD driver. I will send a patch with the changes you suggested. 

Yes, that is what platform data is for.

> Thank you!

NP.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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