linux-kernel - Re: [PATCH v5 2/2] phy: cadence-torrent: Use kernel PHY API to set PHY attributes

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Message-ID: <20200902002956.GE14351@pendragon.ideasonboard.com>
Date:   Wed, 2 Sep 2020 03:29:56 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Swapnil Jakhade <sjakhade@...ence.com>
Cc:     vkoul@...nel.org, kishon@...com, linux-kernel@...r.kernel.org,
        maxime@...no.tech, mparab@...ence.com, yamonkar@...ence.com,
        nsekhar@...com, tomi.valkeinen@...com, jsarha@...com,
        praneeth@...com
Subject: Re: [PATCH v5 2/2] phy: cadence-torrent: Use kernel PHY API to set
 PHY attributes

Hi Swapnil,

Thank you for the patch.

On Mon, Aug 24, 2020 at 08:28:31PM +0200, Swapnil Jakhade wrote:
> Use generic PHY framework function phy_set_attrs() to set number
> of lanes and maximum link rate supported by PHY.
> 
> Signed-off-by: Swapnil Jakhade <sjakhade@...ence.com>
> Acked-by: Kishon Vijay Abraham I <kishon@...com>
> ---
>  drivers/phy/cadence/phy-cadence-torrent.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/phy/cadence/phy-cadence-torrent.c b/drivers/phy/cadence/phy-cadence-torrent.c
> index 7116127358ee..eca71467c4a8 100644
> --- a/drivers/phy/cadence/phy-cadence-torrent.c
> +++ b/drivers/phy/cadence/phy-cadence-torrent.c
> @@ -1710,6 +1710,7 @@ static int cdns_torrent_phy_probe(struct platform_device *pdev)
>  	struct cdns_torrent_phy *cdns_phy;
>  	struct device *dev = &pdev->dev;
>  	struct phy_provider *phy_provider;
> +	struct phy_attrs torrent_attr;
>  	const struct of_device_id *match;
>  	struct cdns_torrent_data *data;
>  	struct device_node *child;
> @@ -1852,6 +1853,12 @@ 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);
> +
> +			torrent_attr.bus_width = cdns_phy->phys[node].num_lanes;
> +			torrent_attr.max_link_rate = cdns_phy->max_bit_rate;
> +			torrent_attr.mode = PHY_MODE_DP;
> +
> +			phy_set_attrs(gphy, &torrent_attr);

Why is this better than accessing the attributes manually as follows ?

			gphy->attrs.bus_width = cdns_phy->phys[node].num_lanes;
			gphy->attrs.max_link_rate = cdns_phy->max_bit_rate;
			gphy->attrs.mode = PHY_MODE_DP;

This is called in cdns_torrent_phy_probe(), before the PHY provider is
registered, so nothing can access the PHY yet. What race condition are
you trying to protect against with usage of phy_set_attrs() ?

>  		} else {
>  			dev_err(dev, "Driver supports only PHY_TYPE_DP\n");
>  			ret = -ENOTSUPP;

-- 
Regards,

Laurent Pinchart