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

From: Lee Jones <lee.jones@linaro.org>
To: Codrin.Ciubotariu@microchip.com
Cc: devicetree@vger.kernel.org, alexandre.belloni@bootlin.com,
	richard.genoud@gmail.com, linux-kernel@vger.kernel.org,
	Ludovic.Desroches@microchip.com,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] ARM: dts: at91: add serial MFD sub-node for usart
Date: Mon, 2 Nov 2020 12:29:52 +0000	[thread overview]
Message-ID: <20201102122952.GB4488@dell> (raw)
In-Reply-To: <780303c7-2c32-f2e1-c9ce-1e2ee6bf0533@microchip.com>

On Mon, 02 Nov 2020, Codrin.Ciubotariu@microchip.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?

> This is not ideal, but it's a solution. What I proposed is more 
> flexible, but, as you pointed out, I am not sure it correctly describes 
> the HW, because the decision of whether to use this IP as a serial or a 
> SPI is a configurable one.
> 
> Thanks and best regards,
> Codrin

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