From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.14]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 70B8612BF3D; Thu, 15 Feb 2024 13:36:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.14 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708004179; cv=none; b=gicxQXISt3sKlCxGrWlHZwBJLiK6zMCBbZBMGuW6iDFcgieGjplTrYONMUpPTbGUq1Wd07DZxDHcn9lrnrUCzqQ0niK1dKBSZu/O3JkoD2H12fMOQaEi2Ggw3D2xNRku1lTaTsIg9G2XfXdwJsz52cNj4K6/mdgGD5KAsBzquJI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708004179; c=relaxed/simple; bh=wKwVgYFc688UeLNGciCD/DyW+yTu3pIXDuMz+D2rtjg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=n2rwiaJWTh6ea7Mdp0ixt7Bir3cem8oOcIf2Xs/iDpWbdeqdjA6rY2lEhSlO3kXLNB4jkS6XuUExn84nJ+NmDs0ZBog60mIfltqpbMTrIlVruzlFARa3WsYL5rfyNXNWsvoZwqku91FMGf2uV2BoryTB+5ko/m0lELRRPKsfy+0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=gywuzh24; arc=none smtp.client-ip=192.198.163.14 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="gywuzh24" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1708004178; x=1739540178; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=wKwVgYFc688UeLNGciCD/DyW+yTu3pIXDuMz+D2rtjg=; b=gywuzh24ibV/kWXPBHYJiMDdmkU4YhqjvGX+vlF+C7ro7sF6ZyD4k2NO bSzfEXzdfNygtynjYmtR8EYjlQ9pVDAbSv72QU2tdTqxZXaUeCUwpacDw 3zEXmRJisUDGj4d3s9y1QFY+wFWSezlrMDbi+MPlHMkx2cZBs8LRnsUZ0 8OfQtL9UhvjX1ted14EulZoDb5aJapVj6C9bvb4myy3v2/FcqlKby0qjj AxCHxBTbHnb8tJIM58Pi4lK1GzmMZVO4drQ6l96iIMH9BwgZHn4ArAU/O lmqx5LVIGOZjXxXfJvuYSyLMLk2CVDybrJMWKgGvuFt9l3bmqW4iQoh7V Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10984"; a="2234316" X-IronPort-AV: E=Sophos;i="6.06,161,1705392000"; d="scan'208";a="2234316" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmvoesa108.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Feb 2024 05:36:18 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10984"; a="935667293" X-IronPort-AV: E=Sophos;i="6.06,161,1705392000"; d="scan'208";a="935667293" Received: from smile.fi.intel.com ([10.237.72.54]) by fmsmga001.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Feb 2024 05:36:15 -0800 Received: from andy by smile.fi.intel.com with local (Exim 4.97) (envelope-from ) id 1rabuP-00000004ngF-005z; Thu, 15 Feb 2024 15:36:13 +0200 Date: Thu, 15 Feb 2024 15:36:12 +0200 From: Andy Shevchenko To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Cc: Raag Jadav , jarkko.nikula@linux.intel.com, mika.westerberg@linux.intel.com, lakshmi.sowjanya.d@intel.com, linux-pwm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/5] pwm: dwc: drop redundant error check Message-ID: References: <20240208070529.28562-1-raag.jadav@intel.com> <20240208070529.28562-2-raag.jadav@intel.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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo On Thu, Feb 15, 2024 at 10:22:57AM +0100, Uwe Kleine-König wrote: > On Wed, Feb 14, 2024 at 07:54:58PM +0200, Andy Shevchenko wrote: > > On Wed, Feb 14, 2024 at 06:45:48PM +0100, Uwe Kleine-König wrote: > > > On Thu, Feb 08, 2024 at 07:04:33PM +0200, Andy Shevchenko wrote: > > > > On Thu, Feb 08, 2024 at 08:46:44AM +0100, Uwe Kleine-König wrote: > > > > > On Thu, Feb 08, 2024 at 12:35:25PM +0530, Raag Jadav wrote: > > > > > > pcim_iomap_table() fails only if pcim_iomap_regions() fails. No need to > > > > > > check for failure if the latter is already successful. > > > > > > > > > > Is this really true? pcim_iomap_table() calls devres_alloc_node() which > > > > > might fail if the allocation fails. (Yes, I know > > > > > https://lwn.net/Articles/627419/, but the rule is still to check for > > > > > errors, right?) > > > > > > > > We do not add a dead code to the kernel, right? > > > > > > > > > What am I missing? > > > > > > > > Mysterious ways of the twisted PCI devres code. > > > > Read the above commit message again :-) > > > > > > > > For your convenience I can elaborate. pcim_iomap_table() calls _first_ > > > > devres_find() which _will_ succeed if the pcim_iomap_regions() previously > > > > succeeded. Does it help to understand how it designed? > > > > > > I assume you're saying that after pcim_iomap_regions() succeeded it's > > > already known that pcim_iomap_table() succeeds (because the former > > > already called the latter). > > > > > > I'm still concerned here. I agree that error checking might be skipped > > > if it's clear that no error can happen (the device cannot disappear > > > between these two calls, can it?), > > > > It depends. If you call it in some asynchronous callbacks which may be run > > after PCI device disappears, then indeed, it's problematic. But you probably > > will have much bigger issue at that point already. > > > > In ->probe() it's guaranteed to work as I suggested (assuming properly working > > hardware). > > Assuming properly working hardware allows to drop many error checks :-) Yes, and we have some checks are being not implemented ("dropped"), but here is the thing: this is a PCI device and surprise removal (while it's not possible for the on-die devices) should be handled differently, not related to this code anyway. Malicious hardware is out of scope either. > > > but for me as an uninitiated pci code > > > reader, I wonder about > > > > > > dwc->base = pcim_iomap_table(pci)[0]; > > > > > > without error checking. (OTOH, if pcim_iomap_table() returned NULL, the > > > "[0]" part is already problematic.) > > > > Seems it's your problem, many drivers use the way I suggested. > > > > > I'd like to have a code comment here saying that pcim_iomap_table() > > > won't return NULL. > > > > Why? It's redundant. If you use it, you should know this API. > > So, the bottom line, does this API needs better documentation? > > If a driver author knows it while writing the code, it's obvious. But if > the driver author looks again in 2 years or someone else (e.g. me with > the PWM maintainer hat on and with little pci experience) that knowledge > might be faded. This is widely used pattern. Anybody who works with Git should know how to use `git grep` tool. If in doubts, always can ask in the mailing lists. I still consider it redundant. P.S. That's what you call "bikeshedding" (done by yourself here)? -- With Best Regards, Andy Shevchenko