linux-kernel - [PATCH 07/11] HID: input: calculate resolution for pressure

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Message-ID: <20250714-support-forcepads-v1-7-71c7c05748c9@google.com>
Date: Mon, 14 Jul 2025 15:09:40 +0000
From: Jonathan Denose <jdenose@...gle.com>
To: Jiri Kosina <jikos@...nel.org>, Benjamin Tissoires <bentiss@...nel.org>, 
	Dmitry Torokhov <dmitry.torokhov@...il.com>, Jonathan Corbet <corbet@....net>, 
	Henrik Rydberg <rydberg@...math.org>
Cc: linux-input@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-doc@...r.kernel.org, Angela Czubak <aczubak@...gle.com>, 
	"Sean O'Brien" <seobrien@...gle.com>, Jonathan Denose <jdenose@...gle.com>
Subject: [PATCH 07/11] HID: input: calculate resolution for pressure

From: Angela Czubak <aczubak@...gle.com>

Assume that if the pressure is given in newtons it should be normalized
to grams. If the pressure has no unit do not calculate resolution.

Signed-off-by: Angela Czubak <aczubak@...gle.com>
Co-developed-by: Jonathan Denose <jdenose@...gle.com>
Signed-off-by: Jonathan Denose <jdenose@...gle.com>
---
 drivers/hid/hid-input.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index d42c1fbd20a1cc01c04f93cf10f1d1c18043929c..1d59787bd0c0e251698e2a2944dae1c4a96adefe 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -303,6 +303,19 @@ __s32 hidinput_calc_abs_res(const struct hid_field *field, __u16 code)
 		}
 		break;
 
+	case ABS_PRESSURE:
+	case ABS_MT_PRESSURE:
+		if (field->unit == HID_UNIT_NEWTON) {
+			/* Convert to grams, 1 newton is 101.97 grams */
+			prev = physical_extents;
+			physical_extents *= 10197;
+			if (physical_extents < prev)
+				return 0;
+			unit_exponent -= 2;
+		} else if (field->unit != HID_UNIT_GRAM) {
+			return 0;
+		}
+		break;
 	default:
 		return 0;
 	}

-- 
2.50.0.727.gbf7dc18ff4-goog