linux-kernel - Re: RE: [PATCH v3 1/2] can: m_can: Move mram init to mcan device setup

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Date:   Thu, 24 Nov 2022 15:54:05 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Vivek Yadav <vivek.2311@...sung.com>
Cc:     rcsekar@...sung.com, krzysztof.kozlowski+dt@...aro.org,
        wg@...ndegger.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, pankaj.dubey@...sung.com,
        ravi.patel@...sung.com, alim.akhtar@...sung.com,
        linux-fsd@...la.com, robh+dt@...nel.org, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org,
        aswani.reddy@...sung.com, sriranjani.p@...sung.com
Subject: Re: RE: [PATCH v3 1/2] can: m_can: Move mram init to mcan device
 setup

On 24.11.2022 14:36:48, Vivek Yadav wrote:
> > Why not call the RAM init directly from m_can_chip_config()?
> > 
> m_can_chip_config function is called from m_can open.
> 
> Configuring RAM init every time we open the CAN instance is not
> needed, I think only once during the probe is enough.

That probably depends on you power management. If I add a regulator to
power the external tcan4x5x chip and power it up during open(), I need
to initialize the RAM.

> If message RAM init failed then fifo Transmit and receive will fail
> and there will be no communication. So there is no point to "open and
> Configure CAN chip".

For mmio devices the RAM init will probably not fail. There are return
values and error checking for the SPI attached devices. Where the SPI
communication will fail. However if this is problem, I assume the chip
will not be detected in the first place.

> From my understanding it's better to keep RAM init inside the probe
> and if there is a failure happened goes to CAN probe failure.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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