From patchwork Sat Mar 6 00:26:20 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Doug Anderson X-Patchwork-Id: 394612 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=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 83527C43381 for ; Sat, 6 Mar 2021 00:27:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 488F365081 for ; Sat, 6 Mar 2021 00:27:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229669AbhCFA0u (ORCPT ); Fri, 5 Mar 2021 19:26:50 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49800 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229493AbhCFA0m (ORCPT ); Fri, 5 Mar 2021 19:26:42 -0500 Received: from mail-pg1-x534.google.com (mail-pg1-x534.google.com [IPv6:2607:f8b0:4864:20::534]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 120D5C06175F for ; Fri, 5 Mar 2021 16:26:42 -0800 (PST) Received: by mail-pg1-x534.google.com with SMTP id p21so2449537pgl.12 for ; Fri, 05 Mar 2021 16:26:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=8ioBMuO2igmW4BL3UDTs4zCq3jWXemfM9CQDn/Vb8qk=; b=UyTGutIQgvDw9NddvZT0M7jm5lw13e0rBcAmuLOdh3y4WLpcn4DrE6HTXb05d4kvR2 3XeS6Bcm7gGno8lDvUbVR5XVvi094lQUPwpTS090oK7/Zg4dxdjyENdH3TzXZz86Yle9 1oTDF7ZSjLvj3n26VdEQRPL31+foAmo7vLHaM= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=8ioBMuO2igmW4BL3UDTs4zCq3jWXemfM9CQDn/Vb8qk=; b=oLLV/xiEDKHAWbWNA8ZkaZqEcq+g+8ES3P4O/ovz0nNoZrt/amMcjZ4IFzbDj0mcbd VSCFOUqVN8xdMRu62mSS0ZDSwqpppsQvUdG3tP9vw0C5eDtyDfV/Gq/rUocraaigD/7R ABxCOqCf19YZQP8RGbfjr4UNLxD9Xy+rH3Ak4WXDrp12NO2t+JKJen2A6VfS7Egh232O nCq+U/oOw/GCPqD9wvNCTNMHto+Md590Sg9G998WGscQSsIHbl0XtTWobxwYVfZXBuBp NB2PmKZEJ66D7+H+Jbt//aNbB5HfoHq1zPoW06pC9qY7z/HmPHNy2IiWDYicroPXKIuu ehSw== X-Gm-Message-State: AOAM530SStaNUHvxo4KI8AldAGPWiFAHGV59xRM3D3XgHnbzLkO2+lzP gXH5cW7gz5dle03i34SAxQaBAg== X-Google-Smtp-Source: ABdhPJxIuI1xVSWldNRPbKE21vi/oPh7r05GVS2zHYb//NYvqS5YxTPZ0GeqWuTUjzMikt0VX32vgg== X-Received: by 2002:a62:87c3:0:b029:1ee:761:bb33 with SMTP id i186-20020a6287c30000b02901ee0761bb33mr11367606pfe.52.1614990401431; Fri, 05 Mar 2021 16:26:41 -0800 (PST) Received: from tictac2.mtv.corp.google.com ([2620:15c:202:1:48f0:8f48:7388:d921]) by smtp.gmail.com with ESMTPSA id 192sm3608905pfa.122.2021.03.05.16.26.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Mar 2021 16:26:40 -0800 (PST) From: Douglas Anderson To: "Rafael J . Wysocki" , Rob Clark , Jordan Crouse Cc: Ulf Hansson , Niklas Cassel , Jorge Ramirez-Ortiz , swboyd@chromium.org, linux-arm-msm@vger.kernel.org, Bjorn Andersson , Akhil P Oommen , Douglas Anderson , Srinivas Kandagatla , linux-kernel@vger.kernel.org Subject: [PATCH 1/3] nvmem: core: Add functions to make number reading easy Date: Fri, 5 Mar 2021 16:26:20 -0800 Message-Id: <20210305162546.1.I323dad4343256b48af2be160b84b1e87985cc9be@changeid> X-Mailer: git-send-email 2.30.1.766.gb4fecdf3b7-goog MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org Sometimes the clients of nvmem just want to get a number out of nvmem. They don't want to think about exactly how many bytes the nvmem cell took up. They just want the number. Let's make it easy. In general this concept is useful because nvmem space is precious and usually the fewest bits are allocated that will hold a given value on a given system. However, even though small numbers might be fine on one system that doesn't mean that logically the number couldn't be bigger. Imagine nvmem containing a max frequency for a component. On one system perhaps that fits in 16 bits. On another system it might fit in 32 bits. The code reading this number doesn't care--it just wants the number. We'll provide two functions: nvmem_cell_read_variable_le_u32() and nvmem_cell_read_variable_le_u64(). Comparing these to the existing functions like nvmem_cell_read_u32(): * These new functions have no problems if the value was stored in nvmem in fewer bytes. It's OK to use these function as long as the value stored will fit in 32-bits (or 64-bits). * These functions avoid problems that the earlier APIs had with bit offsets. For instance, you can't use nvmem_cell_read_u32() to read a value has nbits=32 and bit_offset=4 because the nvmem cell must be at least 5 bytes big to hold this value. The new API accounts for this and works fine. * These functions make it very explicit that they assume that the number was stored in little endian format. The old functions made this assumption whenever bit_offset was non-zero (see nvmem_shift_read_buffer_in_place()) but didn't whenever the bit_offset was zero. NOTE: it's assumed that we don't need an 8-bit or 16-bit version of this function. The 32-bit version of the function can be used to read 8-bit or 16-bit data. At the moment, I'm only adding the "unsigned" versions of these functions, but if it ends up being useful someone could add a "signed" version that did 2's complement sign extension. At the moment, I'm only adding the "little endian" versions of these functions. Adding the "big endian" version would require adding "big endian" support to nvmem_shift_read_buffer_in_place(). Signed-off-by: Douglas Anderson Reviewed-by: Srinivas Kandagatla --- This is a logical follow-up to: https://lore.kernel.org/r/20210227002603.3260599-1-dianders@chromium.org/ ...but since it doesn't really share any of the same patches I'm not marking it as a v2. drivers/nvmem/core.c | 95 ++++++++++++++++++++++++++++++++++ include/linux/nvmem-consumer.h | 4 ++ 2 files changed, 99 insertions(+) diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c index a5ab1e0c74cf..635e3131eb5f 100644 --- a/drivers/nvmem/core.c +++ b/drivers/nvmem/core.c @@ -1606,6 +1606,101 @@ int nvmem_cell_read_u64(struct device *dev, const char *cell_id, u64 *val) } EXPORT_SYMBOL_GPL(nvmem_cell_read_u64); +static void *nvmem_cell_read_variable_common(struct device *dev, + const char *cell_id, + size_t max_len, size_t *len) +{ + struct nvmem_cell *cell; + int nbits; + void *buf; + + cell = nvmem_cell_get(dev, cell_id); + if (IS_ERR(cell)) + return cell; + + nbits = cell->nbits; + buf = nvmem_cell_read(cell, len); + nvmem_cell_put(cell); + if (IS_ERR(buf)) + return buf; + + /* + * If nbits is set then nvmem_cell_read() can significantly exaggerate + * the length of the real data. Throw away the extra junk. + */ + if (nbits) + *len = DIV_ROUND_UP(nbits, 8); + + if (*len > max_len) { + kfree(buf); + return ERR_PTR(-ERANGE); + } + + return buf; +} + +/** + * nvmem_cell_read_variable_le_u32() - Read up to 32-bits of data as a little endian number. + * + * @dev: Device that requests the nvmem cell. + * @cell_id: Name of nvmem cell to read. + * @val: pointer to output value. + * + * Return: 0 on success or negative errno. + */ +int nvmem_cell_read_variable_le_u32(struct device *dev, const char *cell_id, + u32 *val) +{ + size_t len; + u8 *buf; + int i; + + buf = nvmem_cell_read_variable_common(dev, cell_id, sizeof(*val), &len); + if (IS_ERR(buf)) + return PTR_ERR(buf); + + /* Copy w/ implicit endian conversion */ + *val = 0; + for (i = 0; i < len; i++) + *val |= buf[i] << (8 * i); + + kfree(buf); + + return 0; +} +EXPORT_SYMBOL_GPL(nvmem_cell_read_variable_le_u32); + +/** + * nvmem_cell_read_variable_le_u64() - Read up to 64-bits of data as a little endian number. + * + * @dev: Device that requests the nvmem cell. + * @cell_id: Name of nvmem cell to read. + * @val: pointer to output value. + * + * Return: 0 on success or negative errno. + */ +int nvmem_cell_read_variable_le_u64(struct device *dev, const char *cell_id, + u64 *val) +{ + size_t len; + u8 *buf; + int i; + + buf = nvmem_cell_read_variable_common(dev, cell_id, sizeof(*val), &len); + if (IS_ERR(buf)) + return PTR_ERR(buf); + + /* Copy w/ implicit endian conversion */ + *val = 0; + for (i = 0; i < len; i++) + *val |= buf[i] << (8 * i); + + kfree(buf); + + return 0; +} +EXPORT_SYMBOL_GPL(nvmem_cell_read_variable_le_u64); + /** * nvmem_device_cell_read() - Read a given nvmem device and cell * diff --git a/include/linux/nvmem-consumer.h b/include/linux/nvmem-consumer.h index 052293f4cbdb..923dada24eb4 100644 --- a/include/linux/nvmem-consumer.h +++ b/include/linux/nvmem-consumer.h @@ -65,6 +65,10 @@ int nvmem_cell_read_u8(struct device *dev, const char *cell_id, u8 *val); int nvmem_cell_read_u16(struct device *dev, const char *cell_id, u16 *val); int nvmem_cell_read_u32(struct device *dev, const char *cell_id, u32 *val); int nvmem_cell_read_u64(struct device *dev, const char *cell_id, u64 *val); +int nvmem_cell_read_variable_le_u32(struct device *dev, const char *cell_id, + u32 *val); +int nvmem_cell_read_variable_le_u64(struct device *dev, const char *cell_id, + u64 *val); /* direct nvmem device read/write interface */ struct nvmem_device *nvmem_device_get(struct device *dev, const char *name);