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 X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E12B3C35DF5 for ; Tue, 25 Feb 2020 12:51:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BDEDC21556 for ; Tue, 25 Feb 2020 12:51:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729843AbgBYMvq (ORCPT ); Tue, 25 Feb 2020 07:51:46 -0500 Received: from mga02.intel.com ([134.134.136.20]:47567 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728913AbgBYMvq (ORCPT ); Tue, 25 Feb 2020 07:51:46 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 25 Feb 2020 04:51:45 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,484,1574150400"; d="scan'208";a="350143106" Received: from lahna.fi.intel.com (HELO lahna) ([10.237.72.163]) by fmsmga001.fm.intel.com with SMTP; 25 Feb 2020 04:51:42 -0800 Received: by lahna (sSMTP sendmail emulation); Tue, 25 Feb 2020 14:51:41 +0200 Date: Tue, 25 Feb 2020 14:51:41 +0200 From: Mika Westerberg To: Nicholas Johnson Cc: "linux-kernel@vger.kernel.org" , Srinivas Kandagatla Subject: Re: [PATCH v1 1/3] nvmem: Add support for write-only instances Message-ID: <20200225125141.GA2667@lahna.fi.intel.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 24, 2020 at 05:42:33PM +0000, Nicholas Johnson wrote: > Mika Westerberg requires write-only nvmem for the Thunderbolt driver. > Refer to 03cd45d2e219 ("thunderbolt: Prevent crash if non-active NVMem > file is read"). Hence, there is at least one real-world use for > write-only nvmem instances. Well, I don't require anything ;-) It is the thunderbolt driver that has one nvmem device that is write-only and it may take advantage of this. > Add support for write-only nvmem instances by changing the nvmem attrs > to 0222 if the .reg_read callback is not populated. > > Add a WARN_ON in case a driver populates neither .reg_read nor > .reg_write because this behaviour should clearly never occur. > > Signed-off-by: Nicholas Johnson > --- > drivers/nvmem/nvmem-sysfs.c | 77 +++++++++++++++++++++++++++++++++---- > 1 file changed, 70 insertions(+), 7 deletions(-) > > diff --git a/drivers/nvmem/nvmem-sysfs.c b/drivers/nvmem/nvmem-sysfs.c > index 9e0c429cd..be3b94f0b 100644 > --- a/drivers/nvmem/nvmem-sysfs.c > +++ b/drivers/nvmem/nvmem-sysfs.c > @@ -147,6 +147,30 @@ static const struct attribute_group *nvmem_ro_dev_groups[] = { > NULL, > }; > > +/* write only permission */ > +static struct bin_attribute bin_attr_wo_nvmem = { > + .attr = { > + .name = "nvmem", > + .mode = 0222, I would say no sysfs attribute should ever be writable by the world. Actually I think maybe we make this one only writeable by root, in other words it would always require ->root_only to be set. > + }, > + .write = bin_attr_nvmem_write, > +}; > + > +static struct bin_attribute *nvmem_bin_wo_attributes[] = { > + &bin_attr_wo_nvmem, > + NULL, > +}; > + > +static const struct attribute_group nvmem_bin_wo_group = { > + .bin_attrs = nvmem_bin_wo_attributes, > + .attrs = nvmem_attrs, > +}; > + > +static const struct attribute_group *nvmem_wo_dev_groups[] = { > + &nvmem_bin_wo_group, > + NULL, > +}; > + > /* default read/write permissions, root only */ > static struct bin_attribute bin_attr_rw_root_nvmem = { > .attr = { > @@ -196,16 +220,50 @@ static const struct attribute_group *nvmem_ro_root_dev_groups[] = { > NULL, > }; > > +/* write only permission, root only */ > +static struct bin_attribute bin_attr_wo_root_nvmem = { > + .attr = { > + .name = "nvmem", > + .mode = 0200, > + }, > + .write = bin_attr_nvmem_write, > +}; > + > +static struct bin_attribute *nvmem_bin_wo_root_attributes[] = { > + &bin_attr_wo_root_nvmem, > + NULL, > +}; > + > +static const struct attribute_group nvmem_bin_wo_root_group = { > + .bin_attrs = nvmem_bin_wo_root_attributes, > + .attrs = nvmem_attrs, > +}; > + > +static const struct attribute_group *nvmem_wo_root_dev_groups[] = { > + &nvmem_bin_wo_root_group, > + NULL, > +}; > + > const struct attribute_group **nvmem_sysfs_get_groups( > struct nvmem_device *nvmem, > const struct nvmem_config *config) > { > - if (config->root_only) > - return nvmem->read_only ? > - nvmem_ro_root_dev_groups : > - nvmem_rw_root_dev_groups; > - > - return nvmem->read_only ? nvmem_ro_dev_groups : nvmem_rw_dev_groups; > + /* > + * If neither reg_read nor reg_write are provided, we cannot use this > + * nvmem entry, as any operation will cause kernel mode NULL reference. > + */ > + WARN_ON(!nvmem->reg_read && !nvmem->reg_write); This should also be documented in kernel-doc of struct nvmem_config. > + > + if (nvmem->reg_read && nvmem->reg_write) > + return config->root_only ? > + nvmem_rw_root_dev_groups : nvmem_rw_dev_groups; > + > + if (nvmem->reg_read && !nvmem->reg_write) > + return config->root_only ? > + nvmem_ro_root_dev_groups : nvmem_ro_dev_groups; > + > + return config->root_only ? > + nvmem_wo_root_dev_groups : nvmem_wo_dev_groups; > } > > /* > @@ -224,11 +282,16 @@ int nvmem_sysfs_setup_compat(struct nvmem_device *nvmem, > if (!config->base_dev) > return -EINVAL; > > - if (nvmem->read_only) { > + if (nvmem->reg_read && !nvmem->reg_write) { > if (config->root_only) > nvmem->eeprom = bin_attr_ro_root_nvmem; > else > nvmem->eeprom = bin_attr_ro_nvmem; > + } else if (!nvmem->reg_read && nvmem->reg_write) { > + if (config->root_only) > + nvmem->eeprom = bin_attr_wo_root_nvmem; > + else > + nvmem->eeprom = bin_attr_wo_nvmem; > } else { > if (config->root_only) > nvmem->eeprom = bin_attr_rw_root_nvmem; > -- > 2.25.1