linux-kernel - Re: [PATCH 5/8] ARM: dts: at91-sama5d27_wlsom1: Set sst26vf064b SPI NOR flash at its maximum frequency

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Message-ID: <a6fe77b6-4ff4-3c91-0c67-a9da5a638e7b@microchip.com>
Date:   Tue, 28 Mar 2023 10:51:05 +0200
From:   Nicolas Ferre <nicolas.ferre@...rochip.com>
To:     <broonie@...nel.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>,
        <alexandre.belloni@...tlin.com>, <claudiu.beznea@...rochip.com>,
        Tudor Ambarus <tudor.ambarus@...aro.org>
CC:     <linux-spi@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mtd@...ts.infradead.org>
Subject: Re: [PATCH 5/8] ARM: dts: at91-sama5d27_wlsom1: Set sst26vf064b SPI
 NOR flash at its maximum frequency

Hi Tudor,

On 17/11/2022 at 11:52, Tudor Ambarus wrote:
> sama5d27-wlsom1 populates an sst26vf064b SPI NOR flash. Its maximum
> operating frequency for 2.7-3.6V is 104 MHz. As the flash is operated
> at 3.3V, increase its maximum supported frequency to 104MHz. The
> increasing of the spi-max-frequency value requires the setting of the
> "CE# Not Active Hold Time", thus set the spi-cs-setup-ns to a value of 7.
> 
> The sst26vf064b datasheet specifies just a minimum value for the
> "CE# Not Active Hold Time" and it advertises it to 5 ns. There's no
> maximum time specified. I determined experimentally that 5 ns for the
> spi-cs-setup-ns is not enough when the flash is operated close to its
> maximum frequency and tests showed that 7 ns is just fine, so set the
> spi-cs-setup-ns dt property to 7.
> 
> With the increase of frequency the reads are now faster with ~37%.
> 
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> ---
>   arch/arm/boot/dts/at91-sama5d27_wlsom1.dtsi | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/boot/dts/at91-sama5d27_wlsom1.dtsi b/arch/arm/boot/dts/at91-sama5d27_wlsom1.dtsi
> index 83bcf9fe0152..20caf40b4755 100644
> --- a/arch/arm/boot/dts/at91-sama5d27_wlsom1.dtsi
> +++ b/arch/arm/boot/dts/at91-sama5d27_wlsom1.dtsi
> @@ -220,7 +220,8 @@ qspi1_flash: flash@0 {
>   		#size-cells = <1>;
>   		compatible = "jedec,spi-nor";
>   		reg = <0>;
> -		spi-max-frequency = <80000000>;
> +		spi-max-frequency = <104000000>;
> +		spi-cs-setup-ns = /bits/ 16 <7>;

Following the different changes that happened to this property after 
this post, am I right saying that this must now be changed to:

spi-cs-setup-delay-ns = <7>;

?

Thanks for your insight. Best regards,
   Nicolas

>   		spi-rx-bus-width = <4>;
>   		spi-tx-bus-width = <4>;
>   		m25p,fast-read;

-- 
Nicolas Ferre