From patchwork Thu May 20 21:16:56 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vladimir Oltean X-Patchwork-Id: 443816 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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT 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 8F295C43462 for ; Thu, 20 May 2021 21:17:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5F3766135B for ; Thu, 20 May 2021 21:17:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230101AbhETVSa (ORCPT ); Thu, 20 May 2021 17:18:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35634 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229999AbhETVS3 (ORCPT ); Thu, 20 May 2021 17:18:29 -0400 Received: from mail-ej1-x629.google.com (mail-ej1-x629.google.com [IPv6:2a00:1450:4864:20::629]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E47B5C061761; Thu, 20 May 2021 14:17:06 -0700 (PDT) Received: by mail-ej1-x629.google.com with SMTP id lz27so27422842ejb.11; Thu, 20 May 2021 14:17:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=FHUJtBq9iJ9xTw4W3wJ7q5IXipUFvoldRp8Yq4IjtY4=; b=vg1hV+0PHwEzEHpXPgOZmcvjNN3J1pjEPSOcQsZbO4qMpdbVl98MciGQCnU+GTUJmd LTqk+l8GmupW4CNnNal5Wi13nwEpOLm1LO7kvymWDLz3ME98o8V6E8EknC0MH+pWgZWK x/DrCbTj7mDz4KJ5YdJ+xU3mhXN6N8DDq6O2jzUJYu3ZEkQ3kgInWx6miRN4HWwZ+siP Sb4MEbpr43T6foJPp+RWQg+S195LTlQRzdTPWvKpKzupI6YWHl4hbSmatbKCWH4XAlI8 3rroRuxqehN0vGWrlSOA309YLJGXltrV9Tnczmx1XB68YMY//Nr3L0WuCBh4bHV/e0A6 Bn7g== 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:in-reply-to :references:mime-version:content-transfer-encoding; bh=FHUJtBq9iJ9xTw4W3wJ7q5IXipUFvoldRp8Yq4IjtY4=; b=V47WCE+owtO0l+0FUGrpMwrDB1eF4kTKit2yhTOdwIRwRGlQ3cWir36qftSqGOxTz3 qxh9y0ISYYXRdcuBei49RW3mwnCuFTIssV0f36I+HJJEklxzoCdulrPiafSNm2kczYXE cszaskat/yEPQzAwugQfQFwVcXToK2w2h1QNrEKYctbYJOIgnSTNmnvY7WpIi0xxkRuB aYN8XhA4Kq7UoL2+aFj32jyiA2JAFO0Ljxqi+oOu+qGvoYv2W6sqANUntLiqfE8WT2vk OC/CQVRg1QoIA06yEYW1lCCvaVEW+y0YDLMXWCcLGLLfpyhhJqkBZze2h/KSeBU8gY3m /qPQ== X-Gm-Message-State: AOAM532JMDHI59JOy/DY7hXUkmFB9n4s5+ue0czsfjZ5TfnZE3FuW26b 2/77rg0b8CXd9k/FOOhRGTTXyHoQYU0= X-Google-Smtp-Source: ABdhPJxO5vieBooYtc9DXHoPiBcNf5hLqtffiEZXhBbxcVgykW7tAzJTgZS8P6yo/KmFL8gUAyJWsw== X-Received: by 2002:a17:906:a00e:: with SMTP id p14mr6773226ejy.66.1621545424276; Thu, 20 May 2021 14:17:04 -0700 (PDT) Received: from localhost.localdomain ([188.26.52.84]) by smtp.gmail.com with ESMTPSA id w10sm2084212ejq.48.2021.05.20.14.17.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 May 2021 14:17:03 -0700 (PDT) From: Vladimir Oltean To: Jakub Kicinski , "David S. Miller" , netdev@vger.kernel.org Cc: Florian Fainelli , Andrew Lunn , Vivien Didelot , Mark Brown , linux-spi@vger.kernel.org, Guenter Roeck , Vladimir Oltean Subject: [PATCH v3 net-next 1/2] net: dsa: sja1105: send multiple spi_messages instead of using cs_change Date: Fri, 21 May 2021 00:16:56 +0300 Message-Id: <20210520211657.3451036-2-olteanv@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210520211657.3451036-1-olteanv@gmail.com> References: <20210520211657.3451036-1-olteanv@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Vladimir Oltean The sja1105 driver has been described by Mark Brown as "not using the [ SPI ] API at all idiomatically" due to the use of cs_change: https://patchwork.kernel.org/project/netdevbpf/patch/20210520135031.2969183-1-olteanv@gmail.com/ According to include/linux/spi/spi.h, the chip select is supposed to be asserted for the entire length of a SPI message, as long as cs_change is false for all member transfers. The cs_change flag changes the following: (i) When a non-final SPI transfer has cs_change = true, the chip select should temporarily deassert and then reassert starting with the next transfer. (ii) When a final SPI transfer has cs_change = true, the chip select should remain asserted until the following SPI message. The sja1105 driver only uses cs_change for its first property, to form a single SPI message whose layout can be seen below: this is an entire, single spi_message _______________________________________________________________________________________________ / \ +-------------+---------------+-------------+---------------+ ... +-------------+---------------+ | hdr_xfer[0] | chunk_xfer[0] | hdr_xfer[1] | chunk_xfer[1] | | hdr_xfer[n] | chunk_xfer[n] | +-------------+---------------+-------------+---------------+ ... +-------------+---------------+ cs_change false true false true false false ____________________________ _____________________________ _____________________________ CS line __/ \/ \ ... / \__ The fact of the matter is that spi_max_message_size() has an ambiguous meaning if any non-final transfer has cs_change = true. If the SPI master has a limitation in that it cannot keep the chip select asserted for more than, say, 200 bytes (like the spi-sc18is602), the normal thing for it to do is to implement .max_transfer_size and .max_message_size, and limit both to 200: in the "worst case" where cs_change is always false, then the controller can, indeed, not send messages larger than 200 bytes. But the fact that the SPI controller's max_message_size does not necessarily mean that we cannot send messages larger than that. Notably, if the SPI master special-cases the transfers with cs_change and treats every chip select toggling as an entirely new transaction, then a SPI message can easily exceed that limit. So there is a temptation to ignore the controller's reported max_message_size when using cs_change = true in non-final transfers. But that can lead to false conclusions. As Mark points out, the SPI controller might have a different kind of limitation with the max message size, that has nothing at all to do with how long it can keep the chip select asserted. For example, that might be the case if the device is able to offload the chip select changes to the hardware as part of the data stream, and it packs the entire stream of commands+data (corresponding to a SPI message) into a single DMA transfer that is itself limited in size. So the only thing we can do is avoid ambiguity by not using cs_change at all. Instead of sending a single spi_message, we now send multiple SPI messages as follows: spi_message 0 spi_message 1 spi_message n ____________________________ ___________________________ _____________________________ / \ / \ / \ +-------------+---------------+-------------+---------------+ ... +-------------+---------------+ | hdr_xfer[0] | chunk_xfer[0] | hdr_xfer[1] | chunk_xfer[1] | | hdr_xfer[n] | chunk_xfer[n] | +-------------+---------------+-------------+---------------+ ... +-------------+---------------+ cs_change false true false true false false ____________________________ _____________________________ _____________________________ CS line __/ \/ \ ... / \__ which is clearer because the max_message_size limit is now easier to enforce. What is transmitted on the wire stays, of course, the same. Additionally, because we send no more than 2 transfers at a time, we now avoid dynamic memory allocation too, which might be seen as an improvement by some. Signed-off-by: Vladimir Oltean --- drivers/net/dsa/sja1105/sja1105_spi.c | 52 +++++++-------------------- 1 file changed, 12 insertions(+), 40 deletions(-) diff --git a/drivers/net/dsa/sja1105/sja1105_spi.c b/drivers/net/dsa/sja1105/sja1105_spi.c index f7a1514f81e8..8746e3f158a0 100644 --- a/drivers/net/dsa/sja1105/sja1105_spi.c +++ b/drivers/net/dsa/sja1105/sja1105_spi.c @@ -29,13 +29,6 @@ sja1105_spi_message_pack(void *buf, const struct sja1105_spi_message *msg) sja1105_pack(buf, &msg->address, 24, 4, size); } -#define sja1105_hdr_xfer(xfers, chunk) \ - ((xfers) + 2 * (chunk)) -#define sja1105_chunk_xfer(xfers, chunk) \ - ((xfers) + 2 * (chunk) + 1) -#define sja1105_hdr_buf(hdr_bufs, chunk) \ - ((hdr_bufs) + (chunk) * SJA1105_SIZE_SPI_MSG_HEADER) - /* If @rw is: * - SPI_WRITE: creates and sends an SPI write message at absolute * address reg_addr, taking @len bytes from *buf @@ -46,41 +39,25 @@ static int sja1105_xfer(const struct sja1105_private *priv, sja1105_spi_rw_mode_t rw, u64 reg_addr, u8 *buf, size_t len, struct ptp_system_timestamp *ptp_sts) { + u8 hdr_buf[SJA1105_SIZE_SPI_MSG_HEADER] = {0}; struct sja1105_chunk chunk = { .len = min_t(size_t, len, SJA1105_SIZE_SPI_MSG_MAXLEN), .reg_addr = reg_addr, .buf = buf, }; struct spi_device *spi = priv->spidev; - struct spi_transfer *xfers; + struct spi_transfer xfers[2] = {0}; + struct spi_transfer *chunk_xfer; + struct spi_transfer *hdr_xfer; int num_chunks; int rc, i = 0; - u8 *hdr_bufs; num_chunks = DIV_ROUND_UP(len, SJA1105_SIZE_SPI_MSG_MAXLEN); - /* One transfer for each message header, one for each message - * payload (chunk). - */ - xfers = kcalloc(2 * num_chunks, sizeof(struct spi_transfer), - GFP_KERNEL); - if (!xfers) - return -ENOMEM; - - /* Packed buffers for the num_chunks SPI message headers, - * stored as a contiguous array - */ - hdr_bufs = kcalloc(num_chunks, SJA1105_SIZE_SPI_MSG_HEADER, - GFP_KERNEL); - if (!hdr_bufs) { - kfree(xfers); - return -ENOMEM; - } + hdr_xfer = &xfers[0]; + chunk_xfer = &xfers[1]; for (i = 0; i < num_chunks; i++) { - struct spi_transfer *chunk_xfer = sja1105_chunk_xfer(xfers, i); - struct spi_transfer *hdr_xfer = sja1105_hdr_xfer(xfers, i); - u8 *hdr_buf = sja1105_hdr_buf(hdr_bufs, i); struct spi_transfer *ptp_sts_xfer; struct sja1105_spi_message msg; @@ -129,19 +106,14 @@ static int sja1105_xfer(const struct sja1105_private *priv, chunk.len = min_t(size_t, (ptrdiff_t)(buf + len - chunk.buf), SJA1105_SIZE_SPI_MSG_MAXLEN); - /* De-assert the chip select after each chunk. */ - if (chunk.len) - chunk_xfer->cs_change = 1; + rc = spi_sync_transfer(spi, xfers, 2); + if (rc < 0) { + dev_err(&spi->dev, "SPI transfer failed: %d\n", rc); + return rc; + } } - rc = spi_sync_transfer(spi, xfers, 2 * num_chunks); - if (rc < 0) - dev_err(&spi->dev, "SPI transfer failed: %d\n", rc); - - kfree(hdr_bufs); - kfree(xfers); - - return rc; + return 0; } int sja1105_xfer_buf(const struct sja1105_private *priv,