da: graceful deprecated fallback flag

op-celestia/cli.go

@@ -56,10 +56,13 @@ func CLIFlags(envPrefix string) []cli.Flag {
 		},
 		&cli.BoolFlag{
 			Name:    EthFallbackDisabledFlagName,
-			Usage:   "disable eth fallback",
+			Usage:   "disable eth fallback (deprecated, use FallbackModeFlag instead)",
 			EnvVars: opservice.PrefixEnvVar(envPrefix, "DA_ETH_FALLBACK_DISABLED"),
 			Action: func(c *cli.Context, e bool) error {
-				return fmt.Errorf("this flag is deprecated, use the %s flag and it to %s instead", FallbackModeFlagName, FallbackModeDisabled)
+				if e {
+					return c.Set(FallbackModeFlagName, FallbackModeDisabled)
+				}
+				return nil
 			},
 		},
 		&cli.StringFlag{

op-node/rollup/driver/da.go

@@ -6,10 +6,13 @@ import (
 )
 
 func SetDAClient(cfg celestia.CLIConfig) error {
-	// NOTE: for reading from the DA, the fallback mode doesn't matter
-	// because we always read using blob_data_source.go which is
-	// the most permissive mode.
-	client, err := celestia.NewDAClient(cfg.Rpc, cfg.AuthToken, cfg.Namespace, celestia.FallbackModeBlobData)
+	// NOTE: for reading from the DA, we always read using blob_data_source.go
+	// Based on the calldata prefix, it may either read from the DA or from the L1 chain.
+	// In addition, it always reads from the DA for blobs.
+	// See dataAndHashesFromTxs and DataFromEVMTransactions
+	// The read path is independent of the fallback mode.
+	// Therefore the configuration value for FallbackModeBlobData passed here does not matter.
+	client, err := celestia.NewDAClient(cfg.Rpc, cfg.AuthToken, cfg.Namespace, cfg.FallbackMode)
 	if err != nil {
 		return err
 	}