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

["Vivek Yadav" <vivek.2311@samsung.com>]

> -----Original Message-----
> From: Marc Kleine-Budde <mkl@pengutronix.de>
> Sent: 24 November 2022 20:24
> To: Vivek Yadav <vivek.2311@samsung.com>
> Cc: rcsekar@samsung.com; krzysztof.kozlowski+dt@linaro.org;
> wg@grandegger.com; davem@davemloft.net; edumazet@google.com;
> kuba@kernel.org; pabeni@redhat.com; pankaj.dubey@samsung.com;
> ravi.patel@samsung.com; alim.akhtar@samsung.com; linux-fsd@tesla.com;
> robh+dt@kernel.org; linux-can@vger.kernel.org; netdev@vger.kernel.org;
> linux-kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-
> samsung-soc@vger.kernel.org; devicetree@vger.kernel.org;
> aswani.reddy@samsung.com; sriranjani.p@samsung.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.
> 
Thanks for the clarification,
There is one doubt for which I need clarity if I add ram init in m_can_chip_config.

In the current implementation, m_can_ram_init is added in the probe and m_can_class_resume function.
If I add the ram init function in chip_config which is getting called from m_can_start, then m_can_init_ram will be called two times, once in resume and next from m_can_start also.

Can we add ram init inside the m_can_open function itself?
Because it is independent of m_can resume functionality.

> > 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
> 
> --
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