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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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f377775dc0
Enabling the ARM DCC console and using without a JTAG connection will simply hang the system. Since distros like to turn on all options, this is a reoccurring problem to debug. We can do better by checking if anything is attached and handling characters. There is no way to probe this, so send a newline and check that it is handled. Cc: Paolo Pisati <paolo.pisati@canonical.com> Cc: Tim Gardner <tim.gardner@canonical.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Rob Herring <rob.herring@calxeda.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
128 lines
2.6 KiB
C
128 lines
2.6 KiB
C
/* Copyright (c) 2010, Code Aurora Forum. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 and
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* only version 2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*/
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#include <linux/console.h>
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#include <linux/delay.h>
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#include <linux/err.h>
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#include <linux/init.h>
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#include <linux/moduleparam.h>
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#include <linux/types.h>
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#include <asm/processor.h>
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#include "hvc_console.h"
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/* DCC Status Bits */
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#define DCC_STATUS_RX (1 << 30)
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#define DCC_STATUS_TX (1 << 29)
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static inline u32 __dcc_getstatus(void)
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{
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u32 __ret;
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asm volatile("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg"
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: "=r" (__ret) : : "cc");
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return __ret;
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}
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static inline char __dcc_getchar(void)
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{
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char __c;
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asm volatile("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg"
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: "=r" (__c));
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isb();
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return __c;
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}
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static inline void __dcc_putchar(char c)
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{
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asm volatile("mcr p14, 0, %0, c0, c5, 0 @ write a char"
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: /* no output register */
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: "r" (c));
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isb();
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}
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static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
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{
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int i;
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for (i = 0; i < count; i++) {
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while (__dcc_getstatus() & DCC_STATUS_TX)
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cpu_relax();
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__dcc_putchar(buf[i]);
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}
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return count;
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}
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static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
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{
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int i;
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for (i = 0; i < count; ++i)
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if (__dcc_getstatus() & DCC_STATUS_RX)
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buf[i] = __dcc_getchar();
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else
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break;
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return i;
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}
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static bool hvc_dcc_check(void)
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{
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unsigned long time = jiffies + (HZ / 10);
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/* Write a test character to check if it is handled */
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__dcc_putchar('\n');
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while (time_is_after_jiffies(time)) {
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if (!(__dcc_getstatus() & DCC_STATUS_TX))
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return true;
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}
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return false;
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}
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static const struct hv_ops hvc_dcc_get_put_ops = {
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.get_chars = hvc_dcc_get_chars,
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.put_chars = hvc_dcc_put_chars,
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};
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static int __init hvc_dcc_console_init(void)
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{
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if (!hvc_dcc_check())
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return -ENODEV;
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hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
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return 0;
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}
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console_initcall(hvc_dcc_console_init);
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static int __init hvc_dcc_init(void)
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{
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if (!hvc_dcc_check())
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return -ENODEV;
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hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
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return 0;
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}
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device_initcall(hvc_dcc_init);
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