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SubjectRe: [PATCH 04/10] phy: dphy: Add configuration helpers
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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@bootlin.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



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