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([2a0b:e7c0:0:107::aaaa:69]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-367a0b09da7sm9558923f8f.69.2024.07.07.23.10.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 07 Jul 2024 23:10:19 -0700 (PDT) Message-ID: <5619cca5-6d5b-4682-bbf7-51b851cef37e@kernel.org> Date: Mon, 8 Jul 2024 08:10:17 +0200 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH/RFC v1 1/1] tty: serial: 8250_dma: use sgl with 2 nents to take care of buffer wrap To: Ferry Toth , Greg Kroah-Hartman , John Ogness , =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Cc: neil.armstrong@linaro.org, AlCooper , AlexanderShiyan , AlexandreBelloni , AlexandreTorgue , AlimAkhtar , AndrewMorton , "AneeshKumarK . V" , AngeloGioacchinoDelRegno , BaolinWang , BaruchSiach , BjornAndersson , ClaudiuBeznea , "DavidS . Miller" , FabioEstevam , HammerHsieh , =?UTF-8?Q?Christian_K=C3=B6nig?= , ChristopheLeroy , ChunyanZhang , JeromeBrunet , JonathanHunter , KevinHilman , KonradDybcio , KrzysztofKozlowski , KumaravelThiagarajan , LaxmanDewangan , linux-arm-kernel@lists.infradead.org, linux-arm-msm@vger.kernel.org, "MaciejW . Rozycki" , ManivannanSadhasivam , MartinBlumenstingl , MatthiasBrugger , MaximeCoquelin , MichaelEllerman , MichalSimek , "NaveenN . Rao" , NicolasFerre , NicholasPiggin , OrsonZhai , =?UTF-8?Q?Pali_Roh=C3=A1r?= , PatriceChotard , PeterKorsgaard , RichardGenoud , RussellKing , SaschaHauer , ShawnGuo , StefaniSeibold , SumitSemwal , TaichiSugaya , TakaoOrito , TharunKumarP , ThierryReding , TimurTabi , VineetGupta , MarekSzyprowski , PhilEdworthy References: <20240703212613.56024-1-ftoth@exalondelft.nl> <20240703212613.56024-2-ftoth@exalondelft.nl> 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: <20240703212613.56024-2-ftoth@exalondelft.nl> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 03. 07. 24, 22:56, Ferry Toth wrote: > Previously 8250_dma used a circular xmit->buf as DMA output buffer. This > causes messages that wrap around in the circular buffer to be > transmitted using 2 DMA transfers. Depending on baud rate and processor > load this can cause an interchar gap in the middle of the message. On > the receiving end the gap may cause a short receive timeout, possibly > long enough to terminate a DMA transfer, but too short to restart a > receive DMA transfer in time thus causing a receive buffer overrun. > > This is especially a problem for devices with high speed UARTs (HSU) > where even deep 64 byte FIFO's are not sufficient to handle interrupt > latency. > > The circular buffer has now been replaced by kfifo which requires a SG > list with a single entry, which still causes 2 dma transfers when a wrap > around occurs. Fix this by allowing up to 2 entries in the sgl. As I stated earlier, from the DMA and TTY perspective, this looks all good™. So I welcome this. From the devices perspective, obviously testers needed ;). I believe we can merge this in 6.12-rc1 (or even 6.11-rc1?) and see. So please post a non-RFC patch. Reviewed-by: Jiri Slaby > Signed-off-by: Ferry Toth > --- > drivers/tty/serial/8250/8250_dma.c | 19 ++++++++++--------- > 1 file changed, 10 insertions(+), 9 deletions(-) > > diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c > index 8a353e3cc3dd..d215c494ee24 100644 > --- a/drivers/tty/serial/8250/8250_dma.c > +++ b/drivers/tty/serial/8250/8250_dma.c > @@ -89,7 +89,9 @@ int serial8250_tx_dma(struct uart_8250_port *p) > struct tty_port *tport = &p->port.state->port; > struct dma_async_tx_descriptor *desc; > struct uart_port *up = &p->port; > - struct scatterlist sg; > + struct scatterlist *sg; > + struct scatterlist sgl[2]; > + int i; > int ret; > > if (dma->tx_running) { > @@ -110,18 +112,17 @@ int serial8250_tx_dma(struct uart_8250_port *p) > > serial8250_do_prepare_tx_dma(p); > > - sg_init_table(&sg, 1); > - /* kfifo can do more than one sg, we don't (quite yet) */ > - ret = kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, &sg, 1, > + sg_init_table(sgl, ARRAY_SIZE(sgl)); > + > + ret = kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, sgl, ARRAY_SIZE(sgl), > UART_XMIT_SIZE, dma->tx_addr); > > - /* we already checked empty fifo above, so there should be something */ > - if (WARN_ON_ONCE(ret != 1)) > - return 0; > + dma->tx_size = 0; > > - dma->tx_size = sg_dma_len(&sg); > + for_each_sg(sgl, sg, ret, i) > + dma->tx_size += sg_dma_len(sg); > > - desc = dmaengine_prep_slave_sg(dma->txchan, &sg, 1, > + desc = dmaengine_prep_slave_sg(dma->txchan, sgl, ret, > DMA_MEM_TO_DEV, > DMA_PREP_INTERRUPT | DMA_CTRL_ACK); > if (!desc) { -- js