linux-kernel - Re: [PATCH 6/8] serial: Add Tegra Combined UART driver

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Date:   Sun, 13 May 2018 21:06:37 +0300
From:   Mikko Perttunen <cyndis@...si.fi>
To:     Jassi Brar <jassisinghbrar@...il.com>,
        Mikko Perttunen <mperttunen@...dia.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>, araza@...dia.com,
        Devicetree List <devicetree@...r.kernel.org>,
        linux-serial@...r.kernel.org, linux-tegra@...r.kernel.org,
        ", linux-arm-kernel"@lists.infradead.org,
        linux-mediatek@...ts.infradead.org,
        srv_heupstream <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/8] serial: Add Tegra Combined UART driver

On 05/13/2018 06:36 PM, Jassi Brar wrote:
> On Tue, May 8, 2018 at 5:14 PM, Mikko Perttunen <mperttunen@...dia.com> wrote:
> 
> ....
>>
>> +config SERIAL_TEGRA_TCU
>> +       tristate "NVIDIA Tegra Combined UART"
>> +       depends on ARCH_TEGRA && MAILBOX
>> +       select SERIAL_CORE
>> +       help
>> +         Support for the mailbox-based TCU (Tegra Combined UART) serial port.
>> +         TCU is a virtual serial port that allows multiplexing multiple data
>> +         streams into a single hardware serial port.
>> +
> Maybe make it depend upon TEGRA_HSP_MBOX ?

Yeah, that probably makes more sense. MAILBOX is enough to build it but 
it won't be of any use without TEGRA_HSP_MBOX.

> 
> ......
> 
>> +
>> +static void tegra_tcu_write(const char *s, unsigned int count)
>> +{
>> +       struct tegra_tcu *tcu = tegra_tcu_uart_port.private_data;
>> +       unsigned int written = 0, i = 0;
>> +       bool insert_nl = false;
>> +       uint32_t value = 0;
>> +
>> +       while (i < count) {
>> +               if (insert_nl) {
>> +                       value |= '\n' << (written++ * 8);
>> +                       insert_nl = false;
>> +                       i++;
>> +               } else if (s[i] == '\n') {
>> +                       value |= '\r' << (written++ * 8);
>> +                       insert_nl = true;
>> +               } else {
>> +                       value |= s[i++] << (written++ * 8);
>> +               }
>> +
>> +               if (written == 3) {
>> +                       value |= 3 << 24;
>> +                       value |= BIT(26);
>> +                       mbox_send_message(tcu->tx, &value);
>>
> How is this supposed to work? tegra_hsp_doorbell_send_data() ignores
> the second argument.

The previous patch in the series adds support for what are called 
"shared mailboxes" to the tegra-hsp driver. For these the second 
argument is used.

Thanks,
Mikko

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