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Message-ID: <27906f7b-b137-4af2-aa87-49519495a34d@gmail.com> Date: Wed, 13 Aug 2025 12:50:35 +0200 From: Gabor Juhos <j4g8y7@...il.com> To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com> Cc: Wolfram Sang <wsa@...nel.org>, Wolfram Sang <wsa+renesas@...g-engineering.com>, Andi Shyti <andi.shyti@...nel.org>, Russell King <rmk+kernel@...linux.org.uk>, Andrew Lunn <andrew@...n.ch>, Hanna Hawa <hhhawa@...zon.com>, Robert Marko <robert.marko@...tura.hr>, Linus Walleij <linus.walleij@...aro.org>, linux-i2c@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, Imre Kaloz <kaloz@...nwrt.org>, stable@...r.kernel.org Subject: Re: [PATCH v2 3/3] i2c: pxa: handle 'Early Bus Busy' condition on Armada 3700 2025. 08. 11. 22:31 keltezéssel, Andy Shevchenko írta: > On Mon, Aug 11, 2025 at 09:49:57PM +0200, Gabor Juhos wrote: >> Under some circumstances I2C recovery fails on Armada 3700. At least >> on the Methode uDPU board, removing and replugging an SFP module fails >> often, like this: >> >> [ 36.953127] sfp sfp-eth1: module removed >> [ 38.468549] i2c i2c-1: i2c_pxa: timeout waiting for bus free >> [ 38.486960] sfp sfp-eth1: module MENTECHOPTO POS22-LDCC-KR rev 1.0 sn MNC208U90009 dc 200828 >> [ 38.496867] mvneta d0040000.ethernet eth1: unsupported SFP module: no common interface modes >> [ 38.521448] hwmon hwmon2: temp1_input not attached to any thermal zone >> [ 39.249196] sfp sfp-eth1: module removed >> ... >> [ 292.568799] sfp sfp-eth1: please wait, module slow to respond >> ... >> [ 625.208814] sfp sfp-eth1: failed to read EEPROM: -EREMOTEIO >> >> Note that the 'unsupported SFP module' messages are not relevant. The >> module is used only for testing the I2C recovery funcionality, because >> the error can be triggered easily with this specific one. >> >> Enabling debug in the i2c-pxa driver reveals the following: >> >> [ 82.034678] sfp sfp-eth1: module removed >> [ 90.008654] i2c i2c-1: slave_0x50 error: timeout with active message >> [ 90.015112] i2c i2c-1: msg_num: 2 msg_idx: 0 msg_ptr: 0 >> [ 90.020464] i2c i2c-1: IBMR: 00000003 IDBR: 000000a0 ICR: 000007e0 ISR: 00000802 >> [ 90.027906] i2c i2c-1: log: >> [ 90.030787] >> >> This continues until the retries are exhausted ... >> >> [ 110.192489] i2c i2c-1: slave_0x50 error: exhausted retries >> [ 110.198012] i2c i2c-1: msg_num: 2 msg_idx: 0 msg_ptr: 0 >> [ 110.203323] i2c i2c-1: IBMR: 00000003 IDBR: 000000a0 ICR: 000007e0 ISR: 00000802 >> [ 110.210810] i2c i2c-1: log: >> [ 110.213633] >> >> ... then the whole sequence starts again ... >> >> [ 115.368641] i2c i2c-1: slave_0x50 error: timeout with active message >> >> ... while finally the SFP core gives up: >> >> [ 671.975258] sfp sfp-eth1: failed to read EEPROM: -EREMOTEIO >> >> When we analyze the log, it can be seen that bit 1 and 11 is set in the >> ISR (Interface Status Register). Bit 1 indicates the ACK/NACK status, but >> the purpose of bit 11 is not documented in the driver code unfortunately. >> >> The 'Functional Specification' document of the Armada 3700 SoCs family >> however says that this bit indicates an 'Early Bus Busy' condition. The >> document also notes that whenever this bit is set, it is not possible to >> initiate a transaction on the I2C bus. The observed behaviour corresponds >> to this statement. >> >> Unfortunately, I2C recovery does not help as it never runs in this >> special case. Although the driver checks the busyness of the bus at >> several places, but since it does not consider the A3700 specific bit >> in these checks it can't determine the actual status of the bus correctly >> which results in the errors above. >> >> In order to fix the problem, add a new member to struct 'i2c_pxa' to >> store a controller specific bitmask containing the bits indicating the >> busy status, and use that in the code while checking the actual status >> of the bus. This ensures that the correct status can be determined on >> the Armada 3700 based devices without causing functional changes on >> devices based on other SoCs. >> >> With the change applied, the driver detects the busy condition, and runs >> the recovery process: >> >> [ 742.617312] i2c i2c-1: state:i2c_pxa_wait_bus_not_busy:449: ISR=00000802, ICR=000007e0, IBMR=03 >> [ 742.626099] i2c i2c-1: i2c_pxa: timeout waiting for bus free >> [ 742.631933] i2c i2c-1: recovery: resetting controller, ISR=0x00000802 >> [ 742.638421] i2c i2c-1: recovery: IBMR 0x00000003 ISR 0x00000000 >> >> This clears the EBB bit in the ISR register, so it makes it possible to >> initiate transactions on the I2C bus again. >> >> After this patch, the SFP module used for testing can be removed and >> replugged numerous times without causing the error described at the >> beginning. Previously, the error happened after a few such attempts. >> >> The patch has been tested also with the following kernel versions: >> 5.10.237, 5.15.182, 6.1.138, 6.6.90, 6.12.28, 6.14.6. It improves >> recoverabilty on all of them. > > ... > >> Note: the patch is included in this series for completeness however >> it can be applied independently from the preceding patches. On kernels >> 6.3+, it restores I2C functionality even in itself because it recovers >> the controller from the bad state described in the previous patch. > > Sounds to me like this one should be applied first independently on the > discussion / conclusion on the patch 1. Yes. At least the users would have a working although not optimal solution in the meantime. Regards, Gabor
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