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Tue, 02 Sep 2025 02:02:32 -0700 (PDT) Date: Tue, 2 Sep 2025 12:02:29 +0300 From: Dan Carpenter To: Adrian =?utf-8?Q?Barna=C5=9B?= Cc: Hans de Goede , Mauro Carvalho Chehab , Sakari Ailus , Andy Shevchenko , Greg Kroah-Hartman , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, linux-staging@lists.linux.dev Subject: Re: [RFC] staging: media: atomisp: Simplyfy masking bit logic Message-ID: References: <20250902073841.2338568-1-abarnas@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250902073841.2338568-1-abarnas@google.com> On Tue, Sep 02, 2025 at 07:38:40AM +0000, Adrian Barnaś wrote: > 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). Yeah. The "end - 1" is unfortunate. I guess we accidentally started counting from 1... I looked at how to remove it but got lost. > > 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)); > } nit: white space. Add spaces. Remove parentheses. These are supposed to be opposites, right? Subword and inverse Subword. You could dress them up to make them look more opposite. return (w & __GENMASK_ULL(end - 1, start)) >> start; return w & ~__GENMASK_ULL(end - 1, start); regards, dan carpenter