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[81.229.40.193]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5be3739b5d1sm905465e87.22.2026.10.15.04.02.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Oct 2026 04:02:29 -0700 (PDT) From: Marcus Folkesson Subject: [PATCH v13 0/8] I2C Mux per channel bus speed Date: Thu, 15 Oct 2026 13:01:47 +0200 Message-Id: <20261015-i2c-mux-v13-0-778a12cfe93b@gmail.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="utf-8" Content-Transfer-Encoding: 7bit X-B4-Tracking: v=1; b=H4sIAAAAAAAC/2XSy07DMBAF0F+psiZoZvwcVvwHYuHHpLVEW5RCV FT133EqaKxmacvn+mo0l+4kY5FT97K5dKNM5VSOh3pA9bTp0i4cttKXXC86AjLAqPpCqd9/n/s IYFUWCqJzV19/jjKU8y3q7b2ed+X0dRx/bskTzrd/GUT3jAl76Mkn1sEisILX7T6Uj+d03Hdzx kR3hwCNo+qiZW+sTpmNfXSqcQSLU9Ux+JBMGmoR9ej0v7OA5Benq8simpOQs2nV0yyOmhlNpro hUooDs+O4+s+2zi7Ozj2jkJc0ZCcr5xpHzX+uOknORELt0IdH5xenUC/O33qiUz7oPMDKceOoc VydIaYIFjzpVU+EBTpoBopQJXBOAVTyAc1KYiPbkeK8M45i9GHwIj6tJLWSGzlvTTCAkC2pYFw rr9frL69fuvsNAwAA X-Change-ID: 20250913-i2c-mux-b0063de2ae4d To: Wolfram Sang , Michael Hennerich , Bartosz Golaszewski , Andi Shyti , Andy Shevchenko , Bartosz Golaszewski , Peter Rosin , Peter Rosin Cc: linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Marcus Folkesson , Bartosz Golaszewski X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=6441; i=marcus.folkesson@gmail.com; h=from:subject:message-id; bh=euQQtVd/BkM8M86t1ev+NxS3ppr2DdnDQ0Zttt7cQ6g=; b=owEBbQKS/ZANAwAKAYiATm9ZXVIyAcsmYgBq0LKdMyFsR7fqPper1zTmeTEdklbNmw1vy1al5 hX3IyJ3x1OJAjMEAAEKAB0WIQQFUaLotmy1TWTBLGWIgE5vWV1SMgUCatCynQAKCRCIgE5vWV1S MnDbD/sHTPyzlN8rCAFJ5PJ89ack6FbZY7Zm1Ji8y7CJRlHbrJAiT9szD30+tvEsag4iDo74mhW 0fG9D9jcHAsciDIWA9X75coeko85K3KbbPRv3k/FxeMj3svesXWgZPIfYRJhPG04HrrpRQyX2Cp 6vlAL8YxGjxA1wIR+YaK+/TbHa9yz0uii8+n/GBfgzVEbKgQJ8T74cF1AXkxWjJKk3HR/rCiNr8 bYAsaVAQJS9dNY+j2IXa1ZFV+RsRQE8/26wSK+45N6r32tV+TfkSskwYcJ7V60b4yMfXettt/1J omzEM5ZMQ/b13D59FbtcapBKgE7bXzTswCrXGnupiAPHaBpOhOIsBrpUp5xu9belfGSiEn/012b yvQWHk7bOgeSFMrRxnIz9kyaTLlwNZWrN8IAlpM5e2SZMcHn5kMqjbD6oCpXpb8fS4bTsbWG9Fh xj++zbzbhJw40m3lPg7mmil07QLlqrFd0mm66nBStUGfWrGPBMxe2fV8F+HCGmwkIrouJSfAoyv vDrgz/eh63hiRAFi/0dtCpYv6RjGJBepsjzCSx9GIfxzYFACcRcIdfpM1NA+6iKhfOsKpNN8WnV hOxrcSAZdo0GzLeAU/QBkLKtJKsGxHsOKU7jWZBi/21tahISAKvnE4E8VYCS3Pui0lAB4FbC0g5 BAALDZ+WbEGjdSQ== X-Developer-Key: i=marcus.folkesson@gmail.com; a=openpgp; fpr=AB91D46C7E0F6E6FB2AB640EC0FE25D598F6C127 This was a RFC on how to implement a feature to have different bus speeds on different channels with an I2C multiplexer/switch. As no major complaints on the design came up during the review, I decided to submit the series without the RFC tag. The benefit with this feature is that you may group devices after the fastest bus speed they can handle. A real-world example is that you could have e.g. a display running @400kHz and a smart battery running @100kHz using the same I2C controller. There are many corner cases where this may cause a problem for some hardware topologies. I've tried to describe those I could think of in the documentation, see Patch #5. E.g. one risk is that if the mux driver does not disconnect channels when Idle, this may cause a higher frequency to "leak" through to devices that are supposed to run at lower bus speed. This is not only a "problem" for changing bus speed but could also be an issue for potential address conflicts. This patchset has been used and tested heavily the last months on a custom board based on a da850 (DaVinci) platform. The implementation is split up into several patches: Patch #1 Introduce a callback for the i2c controller to set bus speed Patch #2 Introduce functionality to adjust bus speed depending on mux channel. Patch #3 Cleanup i2c-davinci driver a bit to prepare it for set_clk_freq Parch #4 Implement set_clk_freq for the i2c-davinci driver Parch #5 Update documentation with this feature Signed-off-by: Marcus Folkesson --- Changes in v13: - Rebased on i2c-next (7.3-rc7) - Corrected gramatics and wordings - Move set_clk_freq callback to its own structure (i2c_bus_ops) - Fix style issus - Don't leak childs anymore - Link to v12: https://patch.msgid.link/20260719-i2c-mux-v12-0-a5010d623a57@gmail.com Changes in v12: - Defined new idle states in i2c-mux.h - Replaced _hz with _Hz where appropriate - Reword comment and commit message about idle states - Link to v11: https://patch.msgid.link/20260713-i2c-mux-v11-0-72bb8af8ee8c@gmail.com Changes in v11: - Rebased on i2c-next - Use _Hz instead of _hz for local variables in i2c-davinci.c. - Link to v10: https://patch.msgid.link/20260708-i2c-mux-v10-0-09dca03c8a15@gmail.com Changes in v10: - Fix gramatics in documentation - Move {__,}i2c_adapter_set_clk_freq() to i2c-mux.c - Make set_clk_freq() return actual frequency - Reimplement idle_state (from earlier version) - Implement example on idle_state for ltc4306 - Link to v9: https://lore.kernel.org/r/20260324-i2c-mux-v9-0-5292b0608243@gmail.com Changes in v9: - Fix stray blank line - Link to v8: https://lore.kernel.org/r/20260314-i2c-mux-v8-0-fb1738a4df0a@gmail.com Changes in v8: - Fix gramatics and change %d to %u were appropriate - Link to v7: https://lore.kernel.org/r/20260223-i2c-mux-v7-0-ec75b214718a@gmail.com Changes in v7: - Remove code for finding first mux-locked ancestor - Introduce a unlocked (i2c_adapter_set_clk_freq) and unlocked (__i2c_adapter_set_clk_freq) variant - Let the locking be handled in __i2c_adapter_set_clk_freq - Use I2C_MAX_STANDARD_MODE_FREQ instead of magic numbers where appropriate - Link to v6: https://lore.kernel.org/r/20260216-i2c-mux-v6-0-9be28ecfd7e3@gmail.com Changes in v6: - Change logic to find which ancestor to lock with I2C_LOCK_ROOT_ADAPTER It now find the first mux-locked ancestor and then lock its parent. - Remove bus_freq_hz in i2c-davinci and only use clock_hz instead - Mention in commit message that clock_hz can be used to store frequency in an uniform way - Swap order for change freq/deselect to keep symmetry - Only allow bus frequency to be lowered in select() This to not allow an intermediate frequency to be set when it is not supposed to - check if(ret) instead of ret(<0) where appropriate - Fix typos in documentation - Change i2c_adapter.clock_hz from int to u32 - Simplify i2c_adapter_set_clk_freq() by removing 'ret' - Link to v5: https://lore.kernel.org/r/20260213-i2c-mux-v5-0-fb2cbf9979b3@gmail.com Changes in v5: - Take the lock of the top-most mutex locked mux to make sure that the root is locked - Link to v4: https://lore.kernel.org/r/20260128-i2c-mux-v4-0-dee49ce276c0@gmail.com Changes in v4: - Rebase on master - Swap order for printing warning about "channel %u is slower than parent on a non parent-locked mux\n" - Fix typo in comment, adaper->adapter - Link to v3: https://lore.kernel.org/r/20251020-i2c-mux-v3-0-908ac5cf9223@gmail.com Changes in v3: - Return -EINVAL if channel is faster than parent (kernel test robot) - Link to v2: https://lore.kernel.org/r/20251002-i2c-mux-v2-0-b698564cd956@gmail.com Changes in v2: - Changed bus_freq field to bus_freq_hz in davinci_i2c_dev (Bartosz Golaszewski) - Removed idle_state from mux core (Peter Rosin) - Link to v1: https://lore.kernel.org/r/20250922-i2c-mux-v1-0-28c94a610930@gmail.com To: Andi Shyti To: Peter Rosin To: Bartosz Golaszewski To: Michael Hennerich Cc: linux-i2c@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org --- Marcus Folkesson (8): i2c: core: add callback to change bus frequency i2c: mux: add idle_state property to i2c_mux_core i2c: mux: add support for per channel bus frequency i2c: davinci: calculate bus freq from Hz instead of kHz i2c: davinci: add support for setting bus frequency i2c: mux: ltc4306: set correct idle_state in i2c_mux_core docs: i2c: i2c-topology: add section about bus speed i2c: mux: pca954x: use idle state from i2c_mux_core Documentation/i2c/i2c-topology.rst | 180 +++++++++++++++++++++++++++++++++ drivers/i2c/busses/i2c-davinci.c | 39 +++++-- drivers/i2c/i2c-mux.c | 196 +++++++++++++++++++++++++++++++++--- drivers/i2c/muxes/i2c-mux-ltc4306.c | 5 + drivers/i2c/muxes/i2c-mux-pca954x.c | 76 +++++++++----- include/linux/i2c-mux.h | 57 +++++++++++ include/linux/i2c.h | 12 +++ 7 files changed, 518 insertions(+), 47 deletions(-) --- base-commit: a1844c195998e764ed89ceb29a234d2be690f404 change-id: 20250913-i2c-mux-b0063de2ae4d Best regards, -- Marcus Folkesson