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Date: Fri, 19 Feb 2021 10:43:21 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: Al Cooper <alcooperx@...il.com>, linux-kernel@...r.kernel.org
Cc: bcm-kernel-feedback-list@...adcom.com, devicetree@...r.kernel.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-serial@...r.kernel.org, linux-usb@...r.kernel.org,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v3 2/2] serial: 8250: Add new 8250-core based Broadcom STB
driver
On 12. 02. 21, 20:57, Al Cooper wrote:
> Add a UART driver for the new Broadcom 8250 based STB UART. The new
> UART is backward compatible with the standard 8250, but has some
> additional features. The new features include a high accuracy baud
> rate clock system and DMA support.
>
> The driver will use the new optional BAUD MUX clock to select the best
> one of the four master clocks (81MHz, 108MHz, 64MHz and 48MHz) to feed
> the baud rate selection logic for any requested baud rate. This allows
> for more accurate BAUD rates when high speed baud rates are selected.
...
> --- /dev/null
> +++ b/drivers/tty/serial/8250/8250_bcm7271.c
...
> +static void brcmuart_rx_isr(struct uart_port *up, u32 rx_isr)
> +{
> + struct brcmuart_priv *priv = up->private_data;
> + struct device *dev = up->dev;
> + u32 rx_done_isr;
> + u32 check_isr;
> + char seq_err[] = "RX buffer ready out of sequence, restarting RX DMA\n";
What's the purpose of this on-stack variable?
> +static void init_real_clk_rates(struct device *dev, struct brcmuart_priv *priv)
> +{
> + int x;
> + int rc;
> +
> + priv->default_mux_rate = clk_get_rate(priv->baud_mux_clk);
> + dev_dbg(dev, "Default BAUD MUX Clock rate is %lu\n",
> + priv->default_mux_rate);
> +
> + for (x = 0; x < ARRAY_SIZE(priv->real_rates); x++) {
> + if (priv->rate_table[x] == 0) {
> + priv->real_rates[x] = 0;
> + continue;
> + }
> + rc = clk_set_rate(priv->baud_mux_clk, priv->rate_table[x]);
> + if (rc) {
> + dev_err(dev, "Error selecting BAUD MUX clock for %u\n",
> + priv->rate_table[x]);
> + priv->real_rates[x] = priv->rate_table[x];
> + } else {
> + priv->real_rates[x] = clk_get_rate(priv->baud_mux_clk);
> + }
> + }
> + clk_set_rate(priv->baud_mux_clk, priv->default_mux_rate);
This is only weirdly indented.
> +}
> +
> +static void set_clock_mux(struct uart_port *up, struct brcmuart_priv *priv,
> + u32 baud)
> +{
> + u32 percent;
> + u32 best_percent = UINT_MAX;
> + u32 quot;
> + u32 best_quot = 1;
> + u32 rate;
> + int best_index = -1;
> + u64 hires_rate;
> + u64 hires_baud;
> + u64 hires_err;
> + int rc;
> + int i;
> + int real_baud;
> +
> + /* If the Baud Mux Clock was not specified, just return */
> + if (priv->baud_mux_clk == NULL)
> + return;
> +
> + /* Find the closest match for specified baud */
> + for (i = 0; i < ARRAY_SIZE(priv->real_rates); i++) {
> + if (priv->real_rates[i] == 0)
> + continue;
> + rate = priv->real_rates[i] / 16;
> + quot = DIV_ROUND_CLOSEST(rate, baud);
> + if (!quot)
> + continue;
> +
> + /* increase resolution to get xx.xx percent */
> + hires_rate = (u64)rate * 10000;
> + hires_baud = (u64)baud * 10000;
> +
> + hires_err = div_u64(hires_rate, (u64)quot);
> +
> + /* get the delta */
> + if (hires_err > hires_baud)
> + hires_err = (hires_err - hires_baud);
> + else
> + hires_err = (hires_baud - hires_err);
> +
> + percent = (unsigned long)DIV_ROUND_CLOSEST_ULL(hires_err, baud);
> + dev_dbg(up->dev,
> + "Baud rate: %u, MUX Clk: %u, Error: %u.%u%%\n",
> + baud, priv->real_rates[i], percent / 100,
> + percent % 100);
> + if (percent < best_percent) {
> + best_percent = percent;
> + best_index = i;
> + best_quot = quot;
> + }
> + }
> + if (best_index == -1) {
> + dev_err(up->dev, "Error, %d BAUD rate is too fast.\n", baud);
> + return;
> + }
> + rate = priv->real_rates[best_index];
> + rc = clk_set_rate(priv->baud_mux_clk, rate);
> + if (rc)
> + dev_err(up->dev, "Error selecting BAUD MUX clock\n");
> +
> + /* Error over 3 percent will cause data errors */
> + if (best_percent > 300)
> + dev_err(up->dev, "Error, baud: %d has %u.%u%% error\n",
> + baud, percent / 100, percent % 100);
> +
> + real_baud = rate / 16 / best_quot;
> + dev_dbg(up->dev, "Selecting BAUD MUX rate: %u\n", rate);
> + dev_dbg(up->dev, "Requested baud: %u, Actual baud: %u\n",
> + baud, real_baud);
> +
> + /* calc nanoseconds for 1.5 characters time at the given baud rate */
> + i = 1000000000 / real_baud / 10;
NSEC_PER_SEC here?
> + i += (i / 2);
> + priv->char_wait = ns_to_ktime(i);
> +
> + up->uartclk = rate;
> +}
...
> +static int __maybe_unused brcmuart_resume(struct device *dev)
> +{
> + struct brcmuart_priv *priv = dev_get_drvdata(dev);
> + int ret;
> +
> + ret = clk_prepare_enable(priv->baud_mux_clk);
> + if (ret)
> + dev_err(dev, "Error enabling BAUD MUX clock\n");
> +
> + /*
> + * The hardware goes back to it's default after suspend
> + * so get the "clk" back in sync.
> + */
> + ret = clk_set_rate(priv->baud_mux_clk, priv->default_mux_rate);
> + if (ret)
> + dev_err(dev, "Error restoring default BAUD MUX clock\n");
> + if (priv->dma_enabled) {
> + brcmuart_arbitration(priv, 1);
> + brcmuart_init_dma_hardware(priv);
> + start_rx_dma(serial8250_get_port(priv->line));
> + }
> + serial8250_resume_port(priv->line);
All these cannot fail? Or the above can, so does proceeding further
without an error make sense?
> + return 0;
> +}
....
> --- a/drivers/tty/serial/8250/Kconfig
> +++ b/drivers/tty/serial/8250/Kconfig
> @@ -501,6 +501,7 @@ config SERIAL_8250_PXA
> applicable to both devicetree and legacy boards, and early console is
> part of its support.
>
> +
Why adding a newline here?
> config SERIAL_8250_TEGRA
> tristate "8250 support for Tegra serial ports"
> default SERIAL_8250
regards,
--
js
suse labs
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