| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <20241025-spirited-nocturnal-antelope-ce93dd-mkl@pengutronix.de>
Date: Fri, 25 Oct 2024 14:23:55 +0200
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Ming Yu <a0282524688@...il.com>
Cc: tmyu0@...oton.com, lee@...nel.org, linus.walleij@...aro.org,
brgl@...ev.pl, andi.shyti@...nel.org, mailhol.vincent@...adoo.fr,
andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
pabeni@...hat.com, wim@...ux-watchdog.org, linux@...ck-us.net, jdelvare@...e.com,
jic23@...nel.org, lars@...afoo.de, ukleinek@...nel.org,
alexandre.belloni@...tlin.com, linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
linux-i2c@...r.kernel.org, linux-can@...r.kernel.org, netdev@...r.kernel.org,
linux-watchdog@...r.kernel.org, linux-hwmon@...r.kernel.org, linux-iio@...r.kernel.org,
linux-pwm@...r.kernel.org, linux-rtc@...r.kernel.org
Subject: Re: [PATCH v1 1/9] mfd: Add core driver for Nuvoton NCT6694
On 25.10.2024 19:03:55, Ming Yu wrote:
> Oh! I'm sorry about that I confused the packet size.
> The NCT6694 bulk maximum packet size is 256 bytes,
> and USB High speed bulk maximum packet size is 512 bytes.
>
> Marc Kleine-Budde <mkl@...gutronix.de> 於 2024年10月25日 週五 下午6:08寫道：
> >
> > On 25.10.2024 16:08:10, Ming Yu wrote:
> > > > > +int nct6694_read_msg(struct nct6694 *nct6694, u8 mod, u16 offset, u16 length,
> > > > > + u8 rd_idx, u8 rd_len, unsigned char *buf)
> > > >
> > > > why not make buf a void *?
> > >
> > > [Ming] I'll change the type in the next patch.
> > >
> > > >
> > > > > +{
> > > > > + struct usb_device *udev = nct6694->udev;
> > > > > + unsigned char err_status;
> > > > > + int len, packet_len, tx_len, rx_len;
> > > > > + int i, ret;
> > > > > +
> > > > > + mutex_lock(&nct6694->access_lock);
> > > > > +
> > > > > + /* Send command packet to USB device */
> > > > > + nct6694->cmd_buffer[REQUEST_MOD_IDX] = mod;
> > > > > + nct6694->cmd_buffer[REQUEST_CMD_IDX] = offset & 0xFF;
> > > > > + nct6694->cmd_buffer[REQUEST_SEL_IDX] = (offset >> 8) & 0xFF;
> > > > > + nct6694->cmd_buffer[REQUEST_HCTRL_IDX] = HCTRL_GET;
> > > > > + nct6694->cmd_buffer[REQUEST_LEN_L_IDX] = length & 0xFF;
> > > > > + nct6694->cmd_buffer[REQUEST_LEN_H_IDX] = (length >> 8) & 0xFF;
> > > > > +
> > > > > + ret = usb_bulk_msg(udev, usb_sndbulkpipe(udev, BULK_OUT_ENDPOINT),
> > > > > + nct6694->cmd_buffer, CMD_PACKET_SZ, &tx_len,
> > > > > + nct6694->timeout);
> > > > > + if (ret)
> > > > > + goto err;
> > > > > +
> > > > > + /* Receive response packet from USB device */
> > > > > + ret = usb_bulk_msg(udev, usb_rcvbulkpipe(udev, BULK_IN_ENDPOINT),
> > > > > + nct6694->rx_buffer, CMD_PACKET_SZ, &rx_len,
> > > > > + nct6694->timeout);
> > > > > + if (ret)
> > > > > + goto err;
> > > > > +
> > > > > + err_status = nct6694->rx_buffer[RESPONSE_STS_IDX];
> > > > > +
> > > > > + /*
> > > > > + * Segmented reception of messages that exceed the size of USB bulk
> > > > > + * pipe packets.
> > > > > + */
> > > >
> > > > The Linux USB stack can receive bulk messages longer than the max packet size.
> > >
> > > [Ming] Since NCT6694's bulk pipe endpoint size is 128 bytes for this MFD device.
> > > The core will divide packet 256 bytes for high speed USB device, but
> > > it is exceeds
> > > the hardware limitation, so I am dividing it manually.
> >
> > You say the endpoint descriptor is correctly reporting it's max packet
> > size of 128, but the Linux USB will send packets of 256 bytes?
>
> [Ming] The endpoint descriptor is correctly reporting it's max packet
> size of 256, but the Linux USB may send more than 256 (max is 512)
> https://elixir.bootlin.com/linux/v6.11.5/source/drivers/usb/host/xhci-mem.c#L1446
AFAIK according to the USB-2.0 spec the maximum packet size for
high-speed bulk transfers is fixed set to 512 bytes. Does this mean that
your device is a non-compliant USB device?
> > > > > + for (i = 0, len = length; len > 0; i++, len -= packet_len) {
> > > > > + if (len > nct6694->maxp)
> > > > > + packet_len = nct6694->maxp;
> > > > > + else
> > > > > + packet_len = len;
> > > > > +
> > > > > + ret = usb_bulk_msg(udev, usb_rcvbulkpipe(udev, BULK_IN_ENDPOINT),
> > > > > + nct6694->rx_buffer + nct6694->maxp * i,
> > > > > + packet_len, &rx_len, nct6694->timeout);
> > > > > + if (ret)
> > > > > + goto err;
> > > > > + }
> > > > > +
> > > > > + for (i = 0; i < rd_len; i++)
> > > > > + buf[i] = nct6694->rx_buffer[i + rd_idx];
> > > >
> > > > memcpy()?
> > > >
> > > > Or why don't you directly receive data into the provided buffer? Copying
> > > > of the data doesn't make it faster.
> > > >
> > > > On the other hand, receiving directly into the target buffer means the
> > > > target buffer must not live on the stack.
> > >
> > > [Ming] Okay! I'll change it to memcpy().
> >
> > fine!
> >
> > > This is my perspective: the data is uniformly received by the rx_bffer held
> > > by the MFD device. does it need to be changed?
> >
> > My question is: Why do you first receive into the nct6694->rx_buffer and
> > then memcpy() to the buffer provided by the caller, why don't you
> > directly receive into the memory provided by the caller?
>
> [Ming] Due to the bulk pipe maximum packet size limitation, I think consistently
> using the MFD'd dynamically allocated buffer to submit URBs will better
> manage USB-related operations
The non-compliant max packet size limitation is unrelated to the
question which RX or TX buffer to use.
regards,
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
Vertretung Nürnberg | Phone: +49-5121-206917-129 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-9 |
Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)
Powered by blists - more mailing lists