linux-kernel - [PATCH v1] usb: phy: tegra: Add clarifying comments about the shared registers

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Date:   Mon,  3 Feb 2020 01:42:59 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Felipe Balbi <balbi@...nel.org>
Cc:     linux-usb@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v1] usb: phy: tegra: Add clarifying comments about the shared registers

Tools like Coccinelle may erroneously recommend to use the
devm_platform_ioremap_resource() API for the registers mapping because
these tools are not aware about the implementation details of the driver.
Let's add a clarifying comments to the code, which should help to stop
future attempts to break the driver.

Signed-off-by: Dmitry Osipenko <digetx@...il.com>
---
 drivers/usb/phy/phy-tegra-usb.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/usb/phy/phy-tegra-usb.c b/drivers/usb/phy/phy-tegra-usb.c
index 037e8eee737d..6153cc35aba0 100644
--- a/drivers/usb/phy/phy-tegra-usb.c
+++ b/drivers/usb/phy/phy-tegra-usb.c
@@ -969,6 +969,10 @@ static int utmi_phy_probe(struct tegra_usb_phy *tegra_phy,
 		return  -ENXIO;
 	}
 
+	/*
+	 * Note that UTMI pad registers are shared by all PHYs, therefore
+	 * devm_platform_ioremap_resource() can't be used here.
+	 */
 	tegra_phy->pad_regs = devm_ioremap(&pdev->dev, res->start,
 					   resource_size(res));
 	if (!tegra_phy->pad_regs) {
@@ -1087,6 +1091,10 @@ static int tegra_usb_phy_probe(struct platform_device *pdev)
 		return  -ENXIO;
 	}
 
+	/*
+	 * Note that PHY and USB controller are using shared registers,
+	 * therefore devm_platform_ioremap_resource() can't be used here.
+	 */
 	tegra_phy->regs = devm_ioremap(&pdev->dev, res->start,
 				       resource_size(res));
 	if (!tegra_phy->regs) {
-- 
2.24.0