From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A995918E04E; Mon, 4 Nov 2024 06:44:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730702678; cv=none; b=AFHROyxoTaImqtpsk/tVGmNCFBdsS+8fLhFN+U7LRNu72/L+bPiCnD8/jqDKCSPCurr/IsFweaL+SKVbBeVb/q3aICj3zaHaC6Ef7GvV8UfzDesqHYMo3osJgzDwEOvaSb+XoWJdjt1ES4hYqt2m6O8Mi0UIKxuRFjJHpSDj1F0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730702678; c=relaxed/simple; bh=js54YLhYust3jK8sIDaxO+svd/7b/xLRVpzqn3DDqgg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ml6oqNFAK90irJufnw6H3Sbk2ue2dUcJcwG3wpAB5jrPaoBaNgkx0m0lEdbmgloadvmepXTExZO9wkbY182UkE89QR3wcrp+XeVHCwJHdJDXOHIj7O5A6xorWfpXTfPrXNll1J5IsvGpZN/48/aVL3nIxz145j2dcbwSVj3dgLI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=boyuWMU5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="boyuWMU5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 79D0BC4CECE; Mon, 4 Nov 2024 06:44:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1730702678; bh=js54YLhYust3jK8sIDaxO+svd/7b/xLRVpzqn3DDqgg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=boyuWMU5QR8UXjvB/7EDUrlhx3vFtfiu7OAZVAbK0mObJvBu++DfrBFQ/9OVQUHT7 T/uW4GMM5IVrPVi1kLKPSgVVyMTAQpZOFq8pS0vIgcGgOOMvv3F14b6vuTy61boIFE jR8ERhXZ3PHdHfhYbS0yVdDwGp3N4TmuLy2nND7VDoPS1ug495udtE02TBDi8Bpe3Z vB3Yfat+TByUsZrxT8JIf0+rlGlgNcheVPP4pN8QZVEjUerAaCKnJkRq99p2pM7I+4 BEkDThD/eiogI+u72Om7M6ZMHLw6CQqcbRMaYDmHXrcD1TOxB4tdnG1ddfmdhQOiTo vb4hGwVy5BTdA== Message-ID: Date: Mon, 4 Nov 2024 07:44:33 +0100 Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH tty-next v3 1/6] serial: 8250: Adjust the timeout for FIFO mode To: John Ogness , "Maciej W. Rozycki" Cc: Greg Kroah-Hartman , Petr Mladek , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , Esben Haabendal , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Andy Shevchenko , Rengarajan S , Jeff Johnson , Serge Semin , Lino Sanfilippo , Wander Lairson Costa References: <20241025105728.602310-1-john.ogness@linutronix.de> <20241025105728.602310-2-john.ogness@linutronix.de> <837a7ecd-be29-4865-9543-cb6f7e7e46e7@kernel.org> <84sesclkqx.fsf@jogness.linutronix.de> Content-Language: en-US From: Jiri Slaby Autocrypt: addr=jirislaby@kernel.org; keydata= xsFNBE6S54YBEACzzjLwDUbU5elY4GTg/NdotjA0jyyJtYI86wdKraekbNE0bC4zV+ryvH4j rrcDwGs6tFVrAHvdHeIdI07s1iIx5R/ndcHwt4fvI8CL5PzPmn5J+h0WERR5rFprRh6axhOk rSD5CwQl19fm4AJCS6A9GJtOoiLpWn2/IbogPc71jQVrupZYYx51rAaHZ0D2KYK/uhfc6neJ i0WqPlbtIlIrpvWxckucNu6ZwXjFY0f3qIRg3Vqh5QxPkojGsq9tXVFVLEkSVz6FoqCHrUTx wr+aw6qqQVgvT/McQtsI0S66uIkQjzPUrgAEtWUv76rM4ekqL9stHyvTGw0Fjsualwb0Gwdx ReTZzMgheAyoy/umIOKrSEpWouVoBt5FFSZUyjuDdlPPYyPav+hpI6ggmCTld3u2hyiHji2H cDpcLM2LMhlHBipu80s9anNeZhCANDhbC5E+NZmuwgzHBcan8WC7xsPXPaiZSIm7TKaVoOcL 9tE5aN3jQmIlrT7ZUX52Ff/hSdx/JKDP3YMNtt4B0cH6ejIjtqTd+Ge8sSttsnNM0CQUkXps w98jwz+Lxw/bKMr3NSnnFpUZaxwji3BC9vYyxKMAwNelBCHEgS/OAa3EJoTfuYOK6wT6nadm YqYjwYbZE5V/SwzMbpWu7Jwlvuwyfo5mh7w5iMfnZE+vHFwp/wARAQABzSFKaXJpIFNsYWJ5 IDxqaXJpc2xhYnlAa2VybmVsLm9yZz7CwXcEEwEIACEFAlW3RUwCGwMFCwkIBwIGFQgJCgsC BBYCAwECHgECF4AACgkQvSWxBAa0cEnVTg//TQpdIAr8Tn0VAeUjdVIH9XCFw+cPSU+zMSCH eCZoA/N6gitEcnvHoFVVM7b3hK2HgoFUNbmYC0RdcSc80pOF5gCnACSP9XWHGWzeKCARRcQR 4s5YD8I4VV5hqXcKo2DFAtIOVbHDW+0okOzcecdasCakUTr7s2fXz97uuoc2gIBB7bmHUGAH XQXHvdnCLjDjR+eJN+zrtbqZKYSfj89s/ZHn5Slug6w8qOPT1sVNGG+eWPlc5s7XYhT9z66E l5C0rG35JE4PhC+tl7BaE5IwjJlBMHf/cMJxNHAYoQ1hWQCKOfMDQ6bsEr++kGUCbHkrEFwD UVA72iLnnnlZCMevwE4hc0zVhseWhPc/KMYObU1sDGqaCesRLkE3tiE7X2cikmj/qH0CoMWe gjnwnQ2qVJcaPSzJ4QITvchEQ+tbuVAyvn9H+9MkdT7b7b2OaqYsUP8rn/2k1Td5zknUz7iF oJ0Z9wPTl6tDfF8phaMIPISYrhceVOIoL+rWfaikhBulZTIT5ihieY9nQOw6vhOfWkYvv0Dl o4GRnb2ybPQpfEs7WtetOsUgiUbfljTgILFw3CsPW8JESOGQc0Pv8ieznIighqPPFz9g+zSu Ss/rpcsqag5n9rQp/H3WW5zKUpeYcKGaPDp/vSUovMcjp8USIhzBBrmI7UWAtuedG9prjqfO wU0ETpLnhgEQAM+cDWLL+Wvc9cLhA2OXZ/gMmu7NbYKjfth1UyOuBd5emIO+d4RfFM02XFTI t4MxwhAryhsKQQcA4iQNldkbyeviYrPKWjLTjRXT5cD2lpWzr+Jx7mX7InV5JOz1Qq+P+nJW YIBjUKhI03ux89p58CYil24Zpyn2F5cX7U+inY8lJIBwLPBnc9Z0An/DVnUOD+0wIcYVnZAK DiIXODkGqTg3fhZwbbi+KAhtHPFM2fGw2VTUf62IHzV+eBSnamzPOBc1XsJYKRo3FHNeLuS8 f4wUe7bWb9O66PPFK/RkeqNX6akkFBf9VfrZ1rTEKAyJ2uqf1EI1olYnENk4+00IBa+BavGQ 8UW9dGW3nbPrfuOV5UUvbnsSQwj67pSdrBQqilr5N/5H9z7VCDQ0dhuJNtvDSlTf2iUFBqgk 3smln31PUYiVPrMP0V4ja0i9qtO/TB01rTfTyXTRtqz53qO5dGsYiliJO5aUmh8swVpotgK4 /57h3zGsaXO9PGgnnAdqeKVITaFTLY1ISg+Ptb4KoliiOjrBMmQUSJVtkUXMrCMCeuPDGHo7 39Xc75lcHlGuM3yEB//htKjyprbLeLf1y4xPyTeeF5zg/0ztRZNKZicgEmxyUNBHHnBKHQxz 1j+mzH0HjZZtXjGu2KLJ18G07q0fpz2ZPk2D53Ww39VNI/J9ABEBAAHCwV8EGAECAAkFAk6S 54YCGwwACgkQvSWxBAa0cEk3tRAAgO+DFpbyIa4RlnfpcW17AfnpZi9VR5+zr496n2jH/1ld wRO/S+QNSA8qdABqMb9WI4BNaoANgcg0AS429Mq0taaWKkAjkkGAT7mD1Q5PiLr06Y/+Kzdr 90eUVneqM2TUQQbK+Kh7JwmGVrRGNqQrDk+gRNvKnGwFNeTkTKtJ0P8jYd7P1gZb9Fwj9YLx jhn/sVIhNmEBLBoI7PL+9fbILqJPHgAwW35rpnq4f/EYTykbk1sa13Tav6btJ+4QOgbcezWI wZ5w/JVfEJW9JXp3BFAVzRQ5nVrrLDAJZ8Y5ioWcm99JtSIIxXxt9FJaGc1Bgsi5K/+dyTKL wLMJgiBzbVx8G+fCJJ9YtlNOPWhbKPlrQ8+AY52Aagi9WNhe6XfJdh5g6ptiOILm330mkR4g W6nEgZVyIyTq3ekOuruftWL99qpP5zi+eNrMmLRQx9iecDNgFr342R9bTDlb1TLuRb+/tJ98 f/bIWIr0cqQmqQ33FgRhrG1+Xml6UXyJ2jExmlO8JljuOGeXYh6ZkIEyzqzffzBLXZCujlYQ DFXpyMNVJ2ZwPmX2mWEoYuaBU0JN7wM+/zWgOf2zRwhEuD3A2cO2PxoiIfyUEfB9SSmffaK/ S4xXoB6wvGENZ85Hg37C7WDNdaAt6Xh2uQIly5grkgvWppkNy4ZHxE+jeNsU7tg= In-Reply-To: <84sesclkqx.fsf@jogness.linutronix.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 31. 10. 24, 9:49, John Ogness wrote: >>>> + /* Allow timeout for each byte written. */ >>>> + for (i = 0; i < tx_count; i++) { >>>> + if (wait_for_lsr(up, UART_LSR_THRE)) >>> >>> This ensures you sent one character from the FIFO. The FIFO still can contain >>> plenty of them. Did you want UART_LSR_TEMT? >> >> The difference between THRE and TEMT is the state of the shift register >> only[2]: >> >> "In the FIFO mode, TEMT is set when the transmitter FIFO and shift >> register are both empty." > > If we wait for TEMT, we lose significant advantages of having the FIFO. But you wait for THRE, so effectively waiting for FIFO to flush. The difference is only one byte (TSR), or what am I missing? >>> But what's the purpose of spinning _here_? The kernel can run and FIFO >>> too. Without the kernel waiting for the FIFO. > > When serial8250_console_fifo_write() exits, the caller just does a > single wait_for_xmitr() ... with a 10ms timeout. In the FIFO case, for > <=56k baudrates, it can easily hit the timeout and thus continue before > the FIFO has been emptied. >> By waiting on UART_LSR_THRE after filling the FIFO, > serial8250_console_fifo_write() waits until the hardware has had a > chance to shift out all the data. Then the final wait_for_xmitr() in the > caller only waits for the final byte to go out on the line. For the first loop, that's all right. But why would you want to wait for the FIFO to flush at the end of the function? It's not only the last byte, it's the last batch (aka 'tx_count'), right? > Please keep in mind that none of these timeouts should trigger during > normal operation. > > For v4 I am doing some refactoring (as suggested by Andy) so that the > wait-code looks a bit cleaner. OK, let's see then :). thanks, -- js suse labs