linux-kernel - RE: [PATCH] net: stmmac: fix stmmac_pci_probe failed when CONFIG_HAVE

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Date:	Tue, 23 Sep 2014 01:16:12 +0000
From:	"Kweh, Hock Leong" <hock.leong.kweh@...el.com>
To:	David Miller <davem@...emloft.net>
CC:	"peppe.cavallaro@...com" <peppe.cavallaro@...com>,
	"rayagond@...avyalabs.com" <rayagond@...avyalabs.com>,
	"vbridgers2013@...il.com" <vbridgers2013@...il.com>,
	"wens@...e.org" <wens@...e.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Ong, Boon Leong" <boon.leong.ong@...el.com>,
	"tobias.johannes.klausmann@....thm.de" 
	<tobias.johannes.klausmann@....thm.de>
Subject: RE: [PATCH] net: stmmac: fix stmmac_pci_probe failed when
 CONFIG_HAVE_CLK is selected

> -----Original Message-----
> From: David Miller [mailto:davem@...emloft.net]
> Sent: Tuesday, September 23, 2014 2:19 AM
> From: Kweh Hock Leong <hock.leong.kweh@...el.com>
> Date: Thu, 18 Sep 2014 20:34:10 +0800
> 
> Giuseppe, Kweh, where are we with this patch?

We are discussing whether this is the correct fix to the issue. Below is the discussion log:

> > Hmm I am not sure this is the right fix. The driver has to fail if the 
> > main clock is not found. Indeed dev_warn has to be changed in dev_err.
> > 
> > Take a look at Documentation/networking/stmmac.txt but I will post 
> > some patch to improve the documentation adding further detail for clocks too.
> > 
> > The the logic behind the code is that the CSR clock will be set at 
> > runtime if in case of priv->plat->clk_csr ==0 or it will be forced to 
> > a fixed value if passed from the platform instead of.
> > IIRC This was required on some platforms time ago.
> > For sure the driver is designed to fail in case of no main clock is found.
> > 
> > Peppe
>
> Hi Peppe,
>
> I understand your point from the code below (at file stmmac_main.c line 2784):
>
> /* If a specific clk_csr value is passed from the platform
>   * this means that the CSR Clock Range selection cannot be
>   * changed at run-time and it is fixed. Viceversa the driver'll try to
>   * set the MDC clock dynamically according to the csr actual
>   * clock input.
>   */
> if (!priv->plat->clk_csr)
>         stmmac_clk_csr_set(priv);
> else
>         priv->clk_csr = priv->plat->clk_csr;
>
>
> I did search through the whole stmmac_main.c file and found that only stmmac_clk_csr_set() 
> function is leveraging the priv->stmmac_clk params for it calculation. By the logic point of view, 
> I do not need priv->stmmac_clk when I got priv->plat->clk_csr. With this thinking, I propose this 
> fix as when the probe get priv->plat->clk_csr, it shouldn't fail if priv->stmmac_clk has the error value.

Hi Peppe, 

Are you trying to tell that if there is a fix CSR clock value, but driver cannot obtain the clk from devm_clk_get()
(even it is not in use), the driver should fail the probe? 

You have a case with this condition:
HW allow SW to discover the STMMAC controller but HW/SW configures not to supply the CLOCK to STMMAC controller?

My understanding to these priv->plat->clk_csr and priv->stmmac_clk is that 1st one is fixed and 2nd one is dynamic.
When fixed value occurs, dynamic one would not be use. Do I understand this correctly?

Thanks.


Regards,
Wilson
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