linux-kernel - Re: [PATCH 04/10] phy: dphy: Add configuration helpers

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Date:   Fri, 07 Sep 2018 17:26:29 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        linux-media@...r.kernel.org,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Chen-Yu Tsai <wens@...e.org>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        Krzysztof Witos <kwitos@...ence.com>,
        Rafal Ciepiela <rafalc@...ence.com>
Subject: Re: [PATCH 04/10] phy: dphy: Add configuration helpers

Hi Maxime,

On Friday, 7 September 2018 16:37:39 EEST Maxime Ripard wrote:
> On Wed, Sep 05, 2018 at 04:46:05PM +0300, Laurent Pinchart wrote:
> > On Wednesday, 5 September 2018 12:16:35 EEST Maxime Ripard wrote:
> >> The MIPI D-PHY spec defines default values and boundaries for most of
> >> the parameters it defines. Introduce helpers to help drivers get
> >> meaningful values based on their current parameters, and validate the
> >> boundaries of these parameters if needed.
> >> 
> >> Signed-off-by: Maxime Ripard <maxime.ripard@...tlin.com>
> >> ---
> >> 
> >>  drivers/phy/Kconfig               |   8 ++-
> >>  drivers/phy/Makefile              |   1 +-
> >>  drivers/phy/phy-core-mipi-dphy.c  | 160 ++++++++++++++++++++++++++++++-
> >>  include/linux/phy/phy-mipi-dphy.h |   6 +-
> >>  4 files changed, 175 insertions(+)
> >>  create mode 100644 drivers/phy/phy-core-mipi-dphy.c

[snip]

> >> diff --git a/drivers/phy/phy-core-mipi-dphy.c
> >> b/drivers/phy/phy-core-mipi-dphy.c new file mode 100644
> >> index 000000000000..6c1ddc7734a2
> >> --- /dev/null
> >> +++ b/drivers/phy/phy-core-mipi-dphy.c
> >> @@ -0,0 +1,160 @@
> >> +/* SPDX-License-Identifier: GPL-2.0 */
> >> +/*
> >> + * Copyright (C) 2013 NVIDIA Corporation
> >> + * Copyright (C) 2018 Cadence Design Systems Inc.
> >> + */
> >> +
> >> +#include <linux/errno.h>
> >> +#include <linux/export.h>
> >> +#include <linux/kernel.h>
> >> +#include <linux/time64.h>
> >> +
> >> +#include <linux/phy/phy.h>
> >> +#include <linux/phy/phy-mipi-dphy.h>
> >> +
> >> +/*
> >> + * Default D-PHY timings based on MIPI D-PHY specification. Derived
> >> from the
> >> + * valid ranges specified in Section 6.9, Table 14, Page 40 of the
> >> D-PHY
> >> + * specification (v1.2) with minor adjustments.
> > 
> > Could you list those adjustments ?
> 
> I will. This was taken from the Tegra DSI driver, so I'm not sure what
> these are exactly, but that should be addressed.
> 
> >> + */
> >> +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.

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.

-- 
Regards,

Laurent Pinchart