From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B6288C433F5 for ; Mon, 25 Oct 2021 12:57:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 98D0E60184 for ; Mon, 25 Oct 2021 12:57:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233391AbhJYM75 (ORCPT ); Mon, 25 Oct 2021 08:59:57 -0400 Received: from mga05.intel.com ([192.55.52.43]:54793 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233315AbhJYM74 (ORCPT ); Mon, 25 Oct 2021 08:59:56 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10147"; a="315846780" X-IronPort-AV: E=Sophos;i="5.87,180,1631602800"; d="scan'208";a="315846780" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Oct 2021 05:57:30 -0700 X-IronPort-AV: E=Sophos;i="5.87,180,1631602800"; d="scan'208";a="485664166" Received: from smile.fi.intel.com ([10.237.72.184]) by orsmga007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Oct 2021 05:57:27 -0700 Received: from andy by smile.fi.intel.com with local (Exim 4.95) (envelope-from ) id 1mezXG-000ceU-FU; Mon, 25 Oct 2021 15:57:06 +0300 Date: Mon, 25 Oct 2021 15:57:06 +0300 From: "andriy.shevchenko" To: "changlianzhi@uniontech.com" Cc: linux-kernel , "dmitry.torokhov" , gregkh , jirislaby , 282827961 <282827961@qq.com> Subject: Re: [PATCH v6] tty: Fix the keyboard led light display problem Message-ID: References: <20211021020511.18016-1-changlianzhi@uniontech.com> <202110250129181502896@uniontech.com> <202110251224440412487@uniontech.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202110251224440412487@uniontech.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 25, 2021 at 12:24:45PM +0800, changlianzhi@uniontech.com wrote: > On Mon, Oct 25, 2021 at 01:29:18AM +0800, changlianzhi@uniontech.com wrote: > > > >>On Thu, Oct 21, 2021 at 10:05:11AM +0800, lianzhi chang wrote: ... > > > >> + unsigned long leds; > > > >> + > > > >> + leds = (unsigned long)ledstate; > > > > > > >Can be one line. > > > > > > >But most important question you are ignoring to answer / address is why do you > > > >use casting? > > > > >>But most important question you are ignoring to answer / address is why do you > > > >>use casting? > > > Casting is used here because: > > > The second parameter of test_bit is "volatile unsigned long *addr" (see constant_test_bit() in /arch/x86/include/asm/bitops.h), but ledstate is an "unsigned int" type. If casting is not used, > > > compile Will report an error. > > > Wait, you are casting pointer to an integer?! > > This is completely wrong in this case! > > Hello, I did not do that. For the complete code, please check the > "patch v6" email I sent earlier. My code is like this: > +static void kbd_update_ledstate(struct input_dev *dev) > +{ > + unsigned long leds; > + > + leds = (unsigned long)ledstate; > + > + if (!!test_bit(LED_NUML, dev->led) != !!test_bit(VC_NUMLOCK, &leds)) > + ledstate ^= BIT(VC_NUMLOCK); > + if (!!test_bit(LED_CAPSL, dev->led) != !!test_bit(VC_CAPSLOCK, &leds)) > + ledstate ^= BIT(VC_CAPSLOCK); > + if (!!test_bit(LED_SCROLLL, dev->led) != !!test_bit(VC_SCROLLOCK, &leds)) > + ledstate ^= BIT(VC_SCROLLOCK); > +} > I mean, the second parameter of test_bit is "volatile unsigned long *addr", > which is a pointer. And ledstate is an unsigned int type, so I defined an > unsigned long type leds, assign the ledstate to the leds after forced > conversion, and then when calling the test_bit function, get the address > of the leds as a parameter. This all is fine, but why casting is needed? I didn't still get. -- With Best Regards, Andy Shevchenko