Hi Maxime,

On Monday, 10 September 2018 17:16:03 EEST Maxime Ripard wrote:

On Fri, Sep 07, 2018 at 05:26:29PM +0300, Laurent Pinchart wrote:

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+ */
+int phy_mipi_dphy_get_default_config(unsigned long pixel_clock,
+				     unsigned int bpp,
+				     unsigned int lanes,
+				     struct phy_configure_opts_mipi_dphy *cfg)
+{
+	unsigned long hs_clk_rate;
+	unsigned long ui;
+
+	if (!cfg)
+		return -EINVAL;

Should we really expect cfg to be NULL ?

It avoids a kernel panic and it's not in a hot patch, so I'd say yes?

A few line below you divide by the lanes parameter without checking
whether it is equal to 0 first, which would also cause issues.

You say that like it would be a bad thing to test for this.

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I believe that invalid values in input parameters should only be handled
explicitly when considered acceptable for the caller to pass such values.
In this case a NULL cfg pointer is a bug in the caller, which would get
noticed during development if the kernel panics.

In the common case, yes. In the case where that pointer is actually
being lost by the caller somewhere down the line and you have to wait
for a while before it happens, then having the driver inoperant
instead of just having a panic seems like the right thing to do.

But why would it happen in the first place ? Why would the pointer be more 
likely here to be NULL than to contain, for instance, an uninitialized value, 
which we don't guard against ?

-- 
Regards,

Laurent Pinchart