mmc: debugfs: Add a restriction to mmc debugfs clock setting

BugLink: https://bugs.launchpad.net/bugs/1826212

commit e5905ff1 upstream.

Clock frequency values written to an mmc host should not be less than
the minimum clock frequency which the mmc host supports.
Signed-off-by: Yuan Juntao <juntaox.yuan@intel.com>
Signed-off-by: Pawel Wodkowski <pawelx.wodkowski@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/mmc/core/debugfs.c

@@ -220,7 +220,7 @@ static int mmc_clock_opt_set(void *data, u64 val)
 	struct mmc_host *host = data;
 
 	/* We need this check due to input value is u64 */
-	if (val > host->f_max)
+	if (val != 0 && (val > host->f_max || val < host->f_min))
 		return -EINVAL;
 
 	mmc_claim_host(host);