  In this paper I introduce a precise constraint on primordial magnetogenesis,
for a generic class of single-field inflationary model followed by small field
excursion below the Planck scale. I also establish a connection between the
magnetic field at the present epoch and primordial gravity waves ($r$) via
non-vanishing CP asymmetry parameter ($\epsilon_{\bf CP}$), which triggers the
leptogenesis scenario. Finally, I explore various hidden cosmophenomenological
features of theoretical CMB B-mode polarization spectra, which can be treated
as a significant probe to put further stringent constraint on low and high
scale small field inflationary models after releasing the Planck B-mode
polarization data.
