linux-kernel - Re: [PATCH linux-next v2 1/4] ARM: at91/dt: add a new DT property to support FIFOs on Atmel USARTs

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Message-ID: <20150618163924.GQ27492@piout.net>
Date:	Thu, 18 Jun 2015 18:39:24 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Cyrille Pitchen <cyrille.pitchen@...el.com>
Cc:	nicolas.ferre@...el.com, gregkh@...uxfoundation.org,
	wenyou.yang@...el.com, ludovic.desroches@...el.com,
	leilei.zhao@...el.com, josh.wu@...el.com,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	galak@...eaurora.org, ijc+devicetree@...lion.org.uk,
	mark.rutland@....com, pawel.moll@....com, robh+dt@...nel.org
Subject: Re: [PATCH linux-next v2 1/4] ARM: at91/dt: add a new DT property to
 support FIFOs on Atmel USARTs

On 11/06/2015 at 18:20:14 +0200, Cyrille Pitchen wrote :
> This patch adds a new DT property, "atmel,fifo-size", to enable and set
> the maximum number of data the RX and TX FIFOs can store on FIFO capable
> USARTs.
> 
> Please be aware that the VERSION register can not be used to guess the
> size of FIFOs. Indeed, for a given hardware version, the USARTs can be
> integrated on Atmel SoCs with different FIFO sizes. Also the
> "atmel,fifo-size" property is optional as older USARTs don't embed FIFO at
> all.
> 
> Besides, the FIFO size can not be read or guessed from other registers:
> When designing the FIFO feature, no dedicated registers were added to
> store this size. Unsed spaces in the I/O register range are limited and
> better reserved for future usages. Instead, the FIFO size of each
> peripheral is documented in the programmer datasheet.
> 
> Finally, on a given SoC, there can be several instances of USART with
> different FIFO sizes. This explain why we'd rather use a dedicated DT
> property than use the "compatible" property.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...el.com>
Acked-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>


-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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