Re: [PATCH libdrm v2] xf86drm: Parse the separate files to retrieve the vendor, ... info

["Nicolai Hähnle" <nhaehnle@gmail.com>]

On 09.11.2016 19:08, Emil Velikov wrote:
> From: Emil Velikov <emil.velikov@collabora.com>
>
> Parsing config sysfs file wakes up the device. The latter of which may
> be slow and isn't required to begin with.
>
> Reading through config is/was required since the revision is not
> available by other means, although with a kernel patch in the way that
> is about to change.
>
> Since returning 0 when one might expect a valid value is a no-go add a
> workaround drmDeviceUseRevisionFile() which one can use to say "I don't
> care if the revision file returns 0."
>
> v2: Complete rework - add new API to control the method, instead of
> changing it underneat the users' feet.
>
> Cc: Michel Dänzer <michel.daenzer@amd.com>
> Cc: Mauro Santos <registo.mailling@gmail.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98502
> Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
> ---
> I don't have a strong preference for/against this or v1.
>
> With this Mesa will require a 2 line patch. With v1 things will get
> fixed magically, when rebuilt against newer libdrm.
>
> Mauro I'll send the mesa patch in a second. Feel free to give it a spin.
>
> Thanks
> ---
>  xf86drm.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  xf86drm.h | 11 ++++++++++
>  2 files changed, 78 insertions(+), 3 deletions(-)
>
> diff --git a/xf86drm.c b/xf86drm.c
> index 52add5e..676effc 100644
> --- a/xf86drm.c
> +++ b/xf86drm.c
> @@ -113,6 +113,13 @@ void drmSetServerInfo(drmServerInfoPtr info)
>      drm_server_info = info;
>  }
>
> +static bool use_revision_file;
> +
> +void drmDeviceUseRevisionFile(void)
> +{
> +    use_revision_file = true;
> +}

I think this API of setting a magic hidden global variable is really nasty.

Can we add new drmGetDevice[s] entry points with a flags parameter and a 
flag (per Michel's suggestion) which says "I don't care about the 
revision ID"? It kind of sucks because they'll have to get a silly name 
like drmGetDevice[s]2, but I think that's still better than magic global 
state.

Cheers,
Nicolai

> +
>  /**
>   * Output a message to stderr.
>   *
> @@ -2946,10 +2953,56 @@ static int drmGetMaxNodeName(void)
>             3 /* length of the node number */;
>  }
>
> -static int drmParsePciDeviceInfo(const char *d_name,
> -                                 drmPciDeviceInfoPtr device)
> -{
>  #ifdef __linux__
> +static int parse_separate_sysfs_files(const char *d_name,
> +                                      drmPciDeviceInfoPtr device)
> +{
> +#define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
> +    static const char *attrs[] = {
> +      "revision", /* XXX: make sure it's always first, see note below */
> +      "vendor",
> +      "device",
> +      "subsystem_vendor",
> +      "subsystem_device",
> +    };
> +    char path[PATH_MAX + 1];
> +    unsigned int data[ARRAY_SIZE(attrs)];
> +    FILE *fp;
> +    int ret;
> +
> +    for (unsigned i = 0; i < ARRAY_SIZE(attrs); i++) {
> +        snprintf(path, PATH_MAX, "/sys/class/drm/%s/device/%s",
> +                 d_name, attrs[i]);
> +        fp = fopen(path, "r");
> +        if (!fp) {
> +            /* Note: First we check the revision, since older kernels
> +             * may not have it. Default to zero in such cases. */
> +            if (i == 0) {
> +                data[i] = 0;
> +                continue;
> +            }
> +            return -errno;
> +        }
> +
> +        ret = fscanf(fp, "%x", &data[i]);
> +        fclose(fp);
> +        if (ret != 1)
> +            return -errno;
> +
> +    }
> +
> +    device->revision_id = data[0] & 0xff;
> +    device->vendor_id = data[1] & 0xffff;
> +    device->device_id = data[2] & 0xffff;
> +    device->subvendor_id = data[3] & 0xffff;
> +    device->subdevice_id = data[4] & 0xffff;
> +
> +    return 0;
> +}
> +
> +static int parse_config_sysfs_file(const char *d_name,
> +                                  drmPciDeviceInfoPtr device)
> +{
>      char path[PATH_MAX + 1];
>      unsigned char config[64];
>      int fd, ret;
> @@ -2971,6 +3024,17 @@ static int drmParsePciDeviceInfo(const char *d_name,
>      device->subdevice_id = config[46] | (config[47] << 8);
>
>      return 0;
> +}
> +#endif
> +
> +static int drmParsePciDeviceInfo(const char *d_name,
> +                                 drmPciDeviceInfoPtr device)
> +{
> +#ifdef __linux__
> +    if (use_revision_file)
> +        return parse_separate_sysfs_files(d_name, device);
> +
> +    return parse_config_sysfs_file(d_name, device);
>  #else
>  #warning "Missing implementation of drmParsePciDeviceInfo"
>      return -EINVAL;
> diff --git a/xf86drm.h b/xf86drm.h
> index 481d882..d1ebc32 100644
> --- a/xf86drm.h
> +++ b/xf86drm.h
> @@ -796,6 +796,17 @@ extern void drmFreeDevice(drmDevicePtr *device);
>  extern int drmGetDevices(drmDevicePtr devices[], int max_devices);
>  extern void drmFreeDevices(drmDevicePtr devices[], int count);
>
> +
> +/**
> + * Force any sequential calls to drmGetDevice/drmGetDevices to use the
> + * revision sysfs file instead of config one. The latter wakes up the device
> + * if powered off.
> + *
> + * A value of 0 will be returned for the revision_id field if the sysfs file
> + * is missing. DO NOT USE THIS if you depend on a correct revision_id.
> + */
> +extern void drmDeviceUseRevisionFile(void);
> +
>  #if defined(__cplusplus)
>  }
>  #endif
>
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