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From:   Swapnil Kashinath Jakhade <sjakhade@cadence.com>
To:     Maxime Ripard <maxime@cerno.tech>,
        Yuti Suresh Amonkar <yamonkar@cadence.com>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kishon@ti.com" <kishon@ti.com>,
        "mark.rutland@arm.com" <mark.rutland@arm.com>,
        "jsarha@ti.com" <jsarha@ti.com>,
        "tomi.valkeinen@ti.com" <tomi.valkeinen@ti.com>,
        "praneeth@ti.com" <praneeth@ti.com>,
        Milind Parab <mparab@cadence.com>
Subject: RE: [PATCH v1 2/2] phy: phy-cadence-torrent: Use PHY kernel APIs to
 set PHY attributes
Thread-Topic: [PATCH v1 2/2] phy: phy-cadence-torrent: Use PHY kernel APIs to
 set PHY attributes
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Date:   Thu, 30 Apr 2020 14:06:20 +0000
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Hi Maxime,

Thank you so much for reviewing the patch. Please see inline reply below.

> -----Original Message-----
> From: Maxime Ripard <maxime@cerno.tech>
> Sent: Wednesday, April 29, 2020 5:58 PM
> To: Yuti Suresh Amonkar <yamonkar@cadence.com>
> Cc: linux-kernel@vger.kernel.org; kishon@ti.com; mark.rutland@arm.com;
> jsarha@ti.com; tomi.valkeinen@ti.com; praneeth@ti.com; Milind Parab
> <mparab@cadence.com>; Swapnil Kashinath Jakhade
> <sjakhade@cadence.com>
> Subject: Re: [PATCH v1 2/2] phy: phy-cadence-torrent: Use PHY kernel APIs=
 to
> set PHY attributes
>=20
> EXTERNAL MAIL
>=20
>=20
> Hi,
>=20
> On Tue, Apr 28, 2020 at 09:10:04AM +0200, Yuti Amonkar wrote:
> > From: Swapnil Jakhade <sjakhade@cadence.com>
> >
> > Use generic PHY framework function phy_set_bus_width() to set number
> > of lanes and function phy_set_max_link_rate() to set maximum link rate
> > supported by PHY.
> >
> > Signed-off-by: Swapnil Jakhade <sjakhade@cadence.com>
>=20
> This should have your SoB.
>=20
> > ---
> >  drivers/phy/cadence/phy-cadence-torrent.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/phy/cadence/phy-cadence-torrent.c
> b/drivers/phy/cadence/phy-cadence-torrent.c
> > index 7116127358ee..b914e5ddf93c 100644
> > --- a/drivers/phy/cadence/phy-cadence-torrent.c
> > +++ b/drivers/phy/cadence/phy-cadence-torrent.c
> > @@ -1852,6 +1852,9 @@ static int cdns_torrent_phy_probe(struct
> platform_device *pdev)
> >  				 cdns_phy->phys[node].num_lanes,
> >  				 cdns_phy->max_bit_rate / 1000,
> >  				 cdns_phy->max_bit_rate % 1000);
> > +
> > +			phy_set_bus_width(gphy, cdns_phy-
> >phys[node].num_lanes);
> > +			phy_set_max_link_rate(gphy, cdns_phy-
> >max_bit_rate);
>=20
> I think what Kishon meant in his previous mail is that it's not really cl=
ear (to
> me at least) how that function would be useful.
>=20
> In this particular case, what would the consumer make of that information=
?
> Does
> the phy needs to be reconfigured based on the max rate being changed?
>=20
> Some phy_configure_opts structures also have a somewhat similar field tha=
t
> can
> be negociated between the provider and the consumer using phy_validate,
> wouldn't
> that be redundant?
>=20
> Most of that discussion can only happen when you've provided a use-case
> for that
> series, so a consumer using it would help greatly there.

Actually, for this particular case, consumer driver will be the Cadence MHD=
P bridge driver
for DisplayPort which is also under review process for upstreaming [1]. So =
this DRM bridge
driver will make use of the PHY APIs phy_get_bus_width() and phy_get_max_li=
nk_rate()
during execution of probe function to get the number of lanes and maximum l=
ink rate
supported by Cadence Torrent PHY. This information is required to set the h=
ost capabilities
in the DRM bridge driver, based on which initial values for DisplayPort lin=
k training will be
determined.
The changes in this PHY patch series are based on suggestions in the review=
 comments in [1]
which asks to use kernel PHY APIs to read these properties instead of direc=
tly accessing PHY
device node. The complete driver and actual use of these APIs can be found =
in [2]. This is how
we are planning to use these APIs.

[1]
https://patchwork.freedesktop.org/patch/355362/?series=3D73996&rev=3D1

[2]
https://github.com/t-c-collab/linux/blob/cdns-mhdp-upstream/drivers/gpu/drm=
/bridge/cdns-mhdp-core.c#L1594

Thanks & regards,
Swapnil

>=20
> Maxime