Re: [Qemu-devel] [RFC PATCH v1 1/2] utils: Add helper to read arm MIDR_EL1 register

[Paolo Bonzini <pbonzini@redhat.com>]

----- Original Message -----
> From: "vijay kilari" <vijay.kilari@gmail.com>
> To: qemu-arm@nongnu.org, "peter maydell" <peter.maydell@linaro.org>, pbonzini@redhat.com
> Cc: qemu-devel@nongnu.org, "Prasun Kapoor" <Prasun.Kapoor@cavium.com>, "vijay kilari" <vijay.kilari@gmail.com>,
> "Vijaya Kumar K" <Vijaya.Kumar@cavium.com>
> Sent: Tuesday, August 2, 2016 12:20:15 PM
> Subject: [RFC PATCH v1 1/2] utils: Add helper to read arm MIDR_EL1 register
> 
> From: Vijaya Kumar K <Vijaya.Kumar@cavium.com>
> 
> Add helper API to read MIDR_EL1 registers to fetch
> cpu identification information. This helps in
> adding errata's and architecture specific features.
> 
> This is implemented only for arm architecture.
> 
> Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@cavium.com>
> ---
>  include/qemu-common.h |    1 +
>  util/Makefile.objs    |    1 +
>  util/cpuinfo.c        |   52
>  +++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 54 insertions(+)
> 
> diff --git a/include/qemu-common.h b/include/qemu-common.h
> index 1f2cb94..62ad674 100644
> --- a/include/qemu-common.h
> +++ b/include/qemu-common.h
> @@ -134,4 +134,5 @@ void page_size_init(void);
>   * returned. */
>  bool dump_in_progress(void);
>  
> +long int qemu_read_cpuid_info(void);

First, please avoid adding to include/qemu-common.h (it really should
go away).

Second, this is too generic a name.  Please call it something like
qemu_read_aarch64_midr_el1.

Third, it's probably a bad idea to call this function from generic code, so
make it static and add the detection function from patch 2/2 already here.
By making it static, it's also possible to define it only if CONFIG_LINUX
is defined; the ThunderX detection will then return false if !CONFIG_LINUX.

Thanks,

Paolo

>  #endif
> diff --git a/util/Makefile.objs b/util/Makefile.objs
> index 96cb1e0..9d25a72 100644
> --- a/util/Makefile.objs
> +++ b/util/Makefile.objs
> @@ -35,3 +35,4 @@ util-obj-y += log.o
>  util-obj-y += qdist.o
>  util-obj-y += qht.o
>  util-obj-y += range.o
> +util-obj-y += cpuinfo.o
> diff --git a/util/cpuinfo.c b/util/cpuinfo.c
> new file mode 100644
> index 0000000..3ba7194
> --- /dev/null
> +++ b/util/cpuinfo.c
> @@ -0,0 +1,52 @@
> +/*
> + * Dealing with arm cpu identification information.
> + *
> + * Copyright (C) 2016 Cavium, Inc.
> + *
> + * Authors:
> + *  Vijaya Kumar K <Vijaya.Kumar@cavium.com>
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2.1
> + * or later.  See the COPYING.LIB file in the top-level directory.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qemu-common.h"
> +#include "qemu/cutils.h"
> +
> +#if defined(__aarch64__)
> +
> +long int qemu_read_cpuid_info(void)
> +{
> +    FILE *fp;
> +    char *buf;
> +    long int midr = 0;
> +#define BUF_SIZE 32
> +
> +    fp = fopen("/sys/devices/system/cpu/cpu0/regs/identification/midr_el1",
> +               "r");
> +    if (!fp) {
> +        return 0;
> +    }
> +
> +    buf = g_malloc0(BUF_SIZE);
> +    if (!buf) {
> +        fclose(fp);
> +        return 0;
> +    }
> +
> +    if (buf != fgets(buf, BUF_SIZE - 1, fp)) {
> +        goto out;
> +    }
> +
> +    if (qemu_strtol(buf, NULL, 0, &midr) < 0) {
> +        goto out;
> +    }
> +
> +out:
> +    g_free(buf);
> +    fclose(fp);
> +
> +    return midr;
> +}
> +#endif
> --
> 1.7.9.5
> 
>