linux-kernel - [RFC] staging: media: atomisp: Simplyfy masking bit logic

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Message-ID: <20250902073841.2338568-1-abarnas@google.com>
Date: Tue,  2 Sep 2025 07:38:40 +0000
From: "Adrian Barnaś" <abarnas@...gle.com>
To: Hans de Goede <hansg@...nel.org>, Mauro Carvalho Chehab <mchehab@...nel.org>, 
	Sakari Ailus <sakari.ailus@...ux.intel.com>, Andy Shevchenko <andy@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Dan Carpenter <dan.carpenter@...aro.org>, 
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-staging@...ts.linux.dev
Cc: "Adrian Barnaś" <abarnas@...gle.com>
Subject: [RFC] staging: media: atomisp: Simplyfy masking bit logic

Simplified masking logic in pci/hive_isp_css_common/host/vmem.c.

---

I have tested this change on whole range of *valid* inputs, and it gives
the same results as before, but this function seems to be little
counter-intuitive as far as start is a (bit index) but end is
(bit index + 1).

It is follow up to: https://lore.kernel.org/linux-staging/20250901091050.1935505-1-abarnas@google.com/
---
 .../staging/media/atomisp/pci/hive_isp_css_common/host/vmem.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/media/atomisp/pci/hive_isp_css_common/host/vmem.c b/drivers/staging/media/atomisp/pci/hive_isp_css_common/host/vmem.c
index 722b684fbc37..9703e39b7497 100644
--- a/drivers/staging/media/atomisp/pci/hive_isp_css_common/host/vmem.c
+++ b/drivers/staging/media/atomisp/pci/hive_isp_css_common/host/vmem.c
@@ -22,14 +22,14 @@ typedef hive_uedge *hive_wide;
 static inline hive_uedge
 subword(hive_uedge w, unsigned int start, unsigned int end)
 {
-	return (w & (((1ULL << (end - 1)) - 1) << 1 | 1)) >> start;
+	return (w & __GENMASK_ULL(end-1, 0)) >> start;
 }
 
 /* inverse subword bits move like this: MSB[xxxx____xxxx]LSB -> MSB[xxxx0000xxxx]LSB */
 static inline hive_uedge
 inv_subword(hive_uedge w, unsigned int start, unsigned int end)
 {
-	return w & (~(((1ULL << (end - 1)) - 1) << 1 | 1) | ((1ULL << start) - 1));
+	return w & (~__GENMASK_ULL(end-1, start));
 }
 
 #define uedge_bits (8 * sizeof(hive_uedge))
-- 
2.51.0.318.gd7df087d1a-goog