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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-490b6d16f0csm59311625e9.15.2026.06.03.05.48.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Jun 2026 05:48:08 -0700 (PDT) Date: Wed, 3 Jun 2026 13:48:06 +0100 From: David Laight To: Andy Shevchenko Cc: Dan Carpenter , Thomas Petazzoni , Andy Shevchenko , Greg Kroah-Hartman , Helge Deller , Thomas Zimmermann , Chintan Patel , dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org Subject: Re: [PATCH] staging: fbtft: Use sysfs_emit_at() to print to sysfs file Message-ID: <20260603134806.69df0b01@pumpkin> In-Reply-To: References: X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-fbdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 3 Jun 2026 10:49:11 +0300 Andy Shevchenko wrote: > On Wed, Jun 03, 2026 at 10:34:21AM +0300, Dan Carpenter wrote: > > This scnprintf() uses the wrong limit. It should be "PAGE_SIZE - len" > > instead of just PAGE_SIZE. We're not going to hit the limit in real > > life since we are printing at most FBTFT_GAMMA_MAX_VALUES_TOTAL (128) > > u32 values, however, it's still worth fixing. > > > > Use sysfs_emit_at() to fix this since this is a sysfs file. > > OK, > Reviewed-by: Andy Shevchenko > > ... > > > for (i = 0; i < par->gamma.num_curves; i++) { > > for (j = 0; j < par->gamma.num_values; j++) > > - len += scnprintf(&buf[len], PAGE_SIZE, > > + len += sysfs_emit_at(buf, len, > > "%04x ", curves[i * par->gamma.num_values + j]); > > Can we switch to use hex_dump_to_buffer() at some point? > That gets hard when you really want to aim for something nearer seq_printf(). Oh, the way the loops in the code are written doesn't look like it gives the compiler much chance of optimising it very well. This is probably equivalent: for (i = par->gamma.num_curves; i--;) { for (j = par->gamma.num_values; j--;) len += sysfs_emit_at(buf, len, "%04x ", *curves++); buf[len - 1] = '\n'; } and will generate much better code. (Although most of the cost inside the snprintf() function - which is horrid.) num_values better be non-zero. -- David