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Date: Tue, 27 Feb 2024 08:58:16 +0200 From: Arturas Moskvinas <arturas.moskvinas@...il.com> To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com> Cc: linus.walleij@...aro.org, brgl@...ev.pl, u.kleine-koenig@...gutronix.de, linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] gpio: 74x164: Enable output pins after registers are reset Hello, On 2/26/24 16:01, Andy Shevchenko wrote: > On Mon, Feb 26, 2024 at 03:46:56PM +0200, Arturas Moskvinas wrote: >> Move output enabling after chip registers are cleared. > Does this fix anything? If so, maybe elaborate a bit the potential behavioural > changes on the real lines. Chip outputs are enabled[1] before actual reset is performed[2] which might cause pin output value to flip flop if previous pin value was set to 1 in chip. Change fixes that behavior by making sure chip is fully reset before all outputs are enabled. Flip-flop can be noticed when module is removed and inserted again and one of the pins was changed to 1 before removal. 100 microsecond flipping is noticeable on oscilloscope (100khz SPI bus). For a properly reset chip - output is enabled around 100 microseconds (on 100khz SPI bus) later during probing process hence should be irrelevant behavioral change. [1] - https://elixir.bootlin.com/linux/v6.7.4/source/drivers/gpio/gpio-74x164.c#L130 [2] - https://elixir.bootlin.com/linux/v6.7.4/source/drivers/gpio/gpio-74x164.c#L150 Arturas Moskvinas
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